Discrete movements of foot epithelium during adhesive locomotion of a land snail

During the adhesive locomotion of land snails a series of short dark transverse bands, called pedal or foot waves, is visible ifa moving snail's ventral surface is observed through a sheet of glass. Moreover, the mucus secreted from the pedal glands and some pedal epithelial cells forms a thin layer which acts as a glue augmenting adherence, while also acting as a lubricant under the moving parts of the snail's foot. The relationships between velocity and the frequency of pedal waves as well as changes in the volume of small air bubbles under foot waves were analyzed by means of digital recordings made through a glass sheet on which the snails were moving. On the ventral surface of a moving snail foot, the adhering parts of the foot constituted about 80% of the total area, while several moving parts only about 20%. The single moving region of the foot (the pedal wave) amounted to about 3% of snail length. The epithelium in the region of the pedal wave was arched above the substrate and was also more wrinkled than the stationary epithelium, which enabled the forward motion of each specific point of epithelium during the passage of a pedal wave above it. The actual area of epithelium engaged by a pedal wave was at least 30% greater than the area of the epithelium as recorded through a glass sheet. In the region of the pedal wave, the tiny subepithelial muscles acting on the epithelium move it up in the front part of the wave, and then down at the end of the wave, operating vertically in relation to the substrate. In the middle part of the wave, the epithelium only moves forward. In summary, during the adhesive locomotion of snails, the horizontal movement of the ventral surface epithelium proceeds as temporally separate phases of upward, forward and downward movement.     

Involvement of pedal peptide in locomotion in Aplysia: modulation of foot muscle contractions

Pedal peptide (Pep) is a 15-amino-acid neuropeptide that is localized within the Aplysia central nervous system (CNS) predominantly to a broad band of neurons in each pedal ganglion. Pep-neurons were identified by intracellular staining and immunocytology or by radioimmunoassay (RIA) of extracts from identified neurons. RIA reveals that 97% of all Pep-like immunoreactivity (IR-Pep) in pedal nerves is found in the three nerves that innervate the foot. Nearly every Pep-neuron sends an axon out at least one of these three nerves. Application of Pep to foot muscle causes an increase in the amplitude and relaxation rate of contractions driven by nerve stimulation or intracellular stimulation of pedal motor neurons. The increase in relaxation rate was the predominant effect. Intracellular recording in "split-foot" preparations reveals that Pep-neurons increase their overall firing rates and fire in bursts with each step during locomotion. Recovery of IR-Pep from foot perfusate following pedal nerve stimulation increases in a frequency-dependent fashion. Thus it appears that one function of Pep-neurons is to modulate foot muscle contractility during locomotion in Aplysia.     

Embryonic development and organogenesis in the snail Marisa cornuarietis (Mesogastropoda: Ampullariidae). V. Development of the nervous system.

The nervous system is ectodermal in origin. All nerve ganglia arise separately by proliferation and later delamination from the ectoderm, not by invagination. They become secondarily connected to one another by commissures and connectives developing as extensions from the peripheral layer of ganglionic nerve cells. Rudiments of the cerebral, pedal, pleural and intestinal (parietal) ganglia arise almost simultaneously at a relatively early stage (Stage V). The cerebral ganglia develop from the ectoderm of the head plates. Rudiments of the pedal and pleural ganglia are separate at their inception. They later fuse (Stage VI) to form a pleuro-pedal ganglionic mass on each side. The 2 intestinal ganglia are symmetrical at the beginning, but they soon lose their symmetry as a result of torsion. The right ganglion crosses to the left over the gut and persists as the supraintestinal ganglion. The left or subintestinal ganglion shifts to the right and forward, and fuses with the right pleural ganglion (Stage VIII), thus obscuring the chiastoneury. The paired buccal and single visceral (abdominal) ganglia start differentiating in Stage VII. The former develop from the ectodermal wall of the stomodaeum, while the visceral ganglion delaminates from the right wall of the visceral sac, then shifts to the left during torsion. The statocysts develop early (Stage V) from 2 ectodermal invaginations on either side of the rudimentary foot. They later separate from the overlying ectoderm and statoconi appear in their lumina. Contrary to earlier reports on related ampullariids, the osphradium proved to be ontogenetically older than the mantle and mantle cavity. It starts differentiating as a thickened ectodermal plate in the right wall of the visceral sac (Stage V). During torsion, it becomes engulfed in the mantle cavity and shifts to the left side, then is carried forward as the mantlegrow. The eyes develop late (Stage IX) as ectodermal invaginations which rapidly separate from the ectoderm to form closed vesicles. Their cells start differentiating before hatching to form the retina, in which pigment is deposited, and the inner cornea. The lens is secreted in the lumen of the eye and grows by addition of concentric layers of secretion.     

两种软体动物神经系统一氧化氮合酶的组织化学定位

运用一氧化氮合酶(NOS)组织化学方法研究了软体动物门双壳纲种类中国蛤蜊和腹足纲种类嫁Qi神经系统中NOS阳性细胞以及阳性纤维的分布。结果表明：在蛤蜊脑神经节腹内侧,每侧约有10-15个细胞呈强NOS阳性反应,其突起也呈强阳性反应,并经脑足神经节进入足神经节的中央纤维网中;足神经节内只有2个细胞呈弱阳性反应,其突起较短,进入足神经节中央纤维网中,但足神经节中,来自脑神经节阳性细胞和外周神经系统的纤维大多呈NOS阳性反应;脏神经节的前内侧部和后外侧部各有一个阳性细胞团,其突起分别进入后闭壳肌水管后外套膜神经和脑脏神经索。脏神经节背侧小细胞层以及联系两侧小细胞层的纤维也呈NOS阳性反应。嫁Qi中枢神经系统各神经节中没有发现NOS阳性胞体存在;脑神经节、足神经节、侧神经节以及脑—侧、脑—足、侧—脏连索中均有反应程度不同的NOS阳性纤维,这些纤维均源于外周神经。与已研究的软体动物比较,嫁Qi和前鳃亚纲其它种类一样,神经系统中NO作为信息分子可能主要存在于感觉神经。而中国蛤蜊的神经系统中一氧化氮作为信息分子则可能参与更广泛的神经调节过程。     

Structural Repair and Functional Recovery Following Cerebral Ganglion Removal in the Pulmonate Snail Melampus

SYNOPSIS. Regeneration of the nervous system of Melampus followingcerebral ganglion removal proceeds through tract, bud, and ganglionstages Each stage can represent a terminal condition in someanimals Early events of regeneration appear to include rolesfor chemotactic and growth-promoting agents and axonal guidanceby preferential adhesion to a connective tissue sheath Thislatter proposed mechanism accounts for the observed sequencein which the neural elements unite in the tract stage and forthe pattern of failures that result when the sheath is disruptedIn the tract stage of regeneration, communication through thesite of the missing ganglion is restored within the centralnervous system, and between neurons of non-excised ganglia andthe denervated periphery Some behavioral recovery results Thebud stage of regeneration is characterized by neuropil developmentand associated swelling at the site of confluence of the tractsSerotonin immunohistochemistry of bud stage preparations andretrograde dye transport via bud nerves show tracts and numeroussynaptic vancosities, but the neuron somata that are labeledare located in other ganglia Ultrastructural examination oflate bud/early ganglion stage tissue reveals the presence ofsmall undifferentiated cells By six to seven months postoperative,some snails have clearly reached a ganglion stage of regenerationcharacterized by the appearance of differentiated neurons withinthe bud The origin of these new neurons is currently under investigation.     

Octopamine boosts snail locomotion: behavioural and cellular analysis

We measured the reduction in locomotion of unrestrained pond snails, Lymnaea stagnalis, subsequent to transdermal application of two selective octopamine antagonists, epinastine and phentolamine. After 3 h in fresh standard snail water following treatment with 4 mM epinastine or 3.5 mM phentolamine, the snails’ speed was reduced to 25 and 56% of the controls (P < 0.001 and P = 0.02, respectively). The snails’ speed decreased as the drug concentration increased. In the isolated CNS, 0.5 mM octopamine increased the firing rate of the pedal A cluster motoneurons, which innervate the cilia of the foot. In normal saline the increase was 26% and in a high magnesium/low calcium saline 22% (P < 0.05 and 0.01, respectively). We conclude that octopamine is likely to modulate snail locomotion, partially through effects on pedal motoneurons.     

扁玉螺中枢神经系统解剖及显微结构观察

对扁玉螺(Neverita didyma)中枢神经系统的大体解剖和显微结构进行了初步研究。结果表明,扁玉螺中枢神经系统包括一对口球神经节、一对脑神经节、一对侧神经节、一对足神经节及一个脏神经节。各神经节均由神经节被膜、胞体区及中央纤维网三部分组成。左右脑神经节之间和左右足神经节之间的联合以及脑-侧、脑-足和侧-足神经节之间的连索均较短。足神经节有明显的分区现象。     

Adaptive design of locomotion and foot form in prosobranch gastropods

A comparison of the locomotor types, speed, tenacity, and foot form of nearly 300 species in 52 families of marine prosobranchs has revealed that foot size and shape and even subtle variations of locomotion affect the speed and strength of adhesion to the substratum.Gastropods inhabiting soft substrata move primarily by pedal cilia or by discontinuous locomotion in which shell and foot move alternately. Both types of movement are accompanied by low tenacity. A specialized type of discontinuous locomotion, namely, leaping, surpasses all other methods of movement in speed. Species with ciliary locomotion have a very large foot while those with discontinuous movement have an exceedingly small foot relative to shell size.The majority of prosobranchs inhabit hard substrata, move by continuous pedal muscular gliding, and have moderately high tenacity during movement. Arhythmic pedal locomotion yields lower maximum speeds and tenacities than do rhythmic pedal waves. Foot size and shape relative to shell length in species with arhythmic locomotion vary from very short and broad to long and narrow. Studies of transects at several temperate and tropical marine littoral stations showed that these species are confined to low littoral or sublittoral habitats that are sheltered from heavy wave action. High speed and tenacity are simultaneously attained only by species with rhythmic pedal waves.Speed and tenacity do not represent competing selective pressures on the size and shape of the foot. Speed increases among species as the foot approaches or exceeds shell length and is highest if the foot is also broad; the greatest tenacities are attained by species with a long, broad foot whose dimensions do not exceed that of the shell. The optimal shape for both high tenacity and speed is a broad foot somewhat shorter than the shell; neither speed nor tenacity are much compromised by this form. In general, only species with rhythmic pedal waves whose foot size and shape approximate the optimal form for high tenacity and speed are found in habitats exposed to much wave action. Long rhythmic waves, moving a large proportion of foot area at once, are in theory energetically more economical than small, very rapid waves resulting in the same overall speed, but experiments showed that tenacity is significantly reduced in gastropods which increase speed by enlarging the waves. The optimal wave pattern of a species should be a balance between the demand for speed with the least expenditure of energy, favored by a pattern of many large waves at once, and the demand for tenacity, favored by a pattern of few and small waves.Retrograde ditaxic waves of elongation are the most common pattern encountered among prosobranchs, and are associated with a large range of foot sizes and shapes. Such waves are at least one third as long as the foot, while direct waves and other waves of compression are frequently much smaller. The range of foot forms of species with waves of compression is restricted, tending to be optimal for high tenacity or to be long and narrow. Waves of compression appear to be a specialization with the potential for maintaining high tenacity even at high speeds since the waves can be very small, and for giving superior speed since they can travel very rapidly.     

Non-synaptic interaction between neurons in molluscs

1. Isolated pedal ganglia of the pteropodial mollusc, Clione limacina, generate a locomotory rhythm. In 30% of the pedal ganglia preparations the locomotory rhythm was not regular, i.e. the locomotor generator worked in “bursts” alternating with periods of low activity.2. The “locomotor bursts” were caused by spontaneous activation of command neurons located in the pedal ganglia.3. A single neuron was extracted from burst-generating preparations by means of the intracellular microelectrode and then its soma was put back, into the initial place between the ganglion cells. Twenty-five percent of the isolated neurons renewed the bursts-related changes in their activity after the insertion into the ganglion. The neurons which were originally excited during the “locomotor bursts” continued to be excited after isolation, while those which were inhibited continued to be inhibited during the bursts.4. It is suggested that the command neurons controlling the locomotor generator can exert action on the target cells in the absence of morphological synapses.     

Somatic polyploidy in neurons of the gastropod molluscs. II. Dynamics of DNA synthesis in the process of postnatal growth of CNS neurons in Succineid snail

A study was made of the age dynamics of polyploidization and dynamics of DNA synthesis in neuron cell nuclei during the postnatal growth of the gastropod pulmonate snail Succinea lauta. According to cytophotometrical results, the degree of polyploidization in neuron nuclei increases from young to adult individuals, varying from 2c to 16,384c. In the visceral complex, the maximum and medium ploidy values of the neuron nuclei are higher by almost 4-8 times than those in cerebral and pedal ganglia. The medium level of ploidy in adult snails increases by 5.7 times in the visceral complex of ganglia and by 4.1-4.2 times in the pedal and cerebral ganglia. According to 3H-thymidine autoradiography, DNA synthesis in neuron nuclei occurs during the whole life of the snail. In young individuals the neurons have the highest activity of DNA synthesis--the index of labeled nuclei of neurons making in total 50.2%. In older age, a steady decrease in the index of labeled nuclei is observed--in total to 35.8% and 7.0% in small and large adult snails, respectively. The state of summer hibernation completely stops DNA syntheses in neurons, but emergency from hibernation is accompanied by restoration of DNA syntheses.     

Locomotor rhythms in the pond snail Lymnaea stagnalis: site of origin and neurotransmitter requirements

1. We have found that, in preparations of isolated CNS of the pond snail Lymnaea stagnalis, both serotonin (5HT) and dopamine (DA), as well as their respective precursors, 5HTP and DOPA, are effective in producing fictive intense (muscular) locomotion. 2. Phase-coupled to each of the above pedal rhythms are numerous identifiable pedal neurons including the respiratory interneuron RPeD1, thus suggesting interaction between networks responsible for locomotion and air breathing. 3. The novel DA/DOPA-dependent motor rhythm resembles the 5HT/5HTP-dependent one in terms of activity of identifiable pedal neurons, being however considerably slower than the latter. 4. The results of transection experiments suggest that each of the rhythms is generated by a paired CPG lying entirely within the pedal ganglia.     

Regeneration of pedal ganglion neurons in the sea butterfly Clione limacina

In the pedal ganglia ofClione limacina the growth of neurites is traced in motoneurons after transection of the wing nerve and in interneurons after transection of the pedal commissure. Neurons were stained intracellularly with Lucifer yellow. In the motoneurons the neurites growing from the transected end of the axon and from the neuron soma spread to all nerve trunks departing from the ipsi- and contralateral ganglia. For nerve transection in the intact mollusk, wing movements were restored 10 days after the operation. In the interneurons the growing neurites branched within the pedal ganglion or spread to the cerebral ganglia, but they never reached the periphery.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 449–455, July–August, 1985.     

Localization of ovulation hormone-like neuropeptide in the central nervous system of the snail Lymnaea stagnalis by means of immunocytochemistry and in situ hybridization

Summary The caudo-dorsal cells (CDC) in the cerebral ganglia of the pond snail Lymnaea stagnalis synthesize the 36-amino acid ovulation hormone (CDCH). We have used immuno-cytochemistry and in situ hybridization to reveal the localization of neurons and axons containing CDCH-like material.A monoclonal antibody to a fragment of CDCH and a cDNA probe encoding CDCH reacted with the CDC-system, with specific cell groups in the cerebral and pleural ganglia, and with individually occurring neurons throughout the central nervous system. The cells in the pleural ganglia, which were found in about 50% of the preparations studied, are considered as ectopic CDC. They are morphologically similar to CDC in their somal dimensions and axonal organization. By means of immuno-electron microscopy it was shown that these neurons contain secretory vesicles that are similar to those of the CDC. The neurons of the bilateral groups occurring in the cerebral ganglia in addition to the CDC are smaller and more intensely stained than the CDC. Axons of these small neurons probably have varicosities located on the CDC axons in the neuropil of the cerebral ganglion, indicating synaptic contacts. Two major axon tracts could be followed from (or toward) the neuropil of the cerebral ganglion. One tract runs from the cerebral gangion via the pleural and parietal ganglia to the visceral ganglion, giving off branches to most nerves emanating from these ganglia. The other tract could be traced through the cerebro-pedal connective to the pedal ganglia. Only in the right pedal ganglion was extensive axonal branching observed. The nerves emanating from this ganglion contained many more immunoreactive axons than those from the left pedal ganglion. A polyclonal antibody raised against the synthetic fragment of CDCH stained, in addition to the neurons and axons revealed with the monoclonal antibody and the cDNA probe, three other major groups of neurons. Two are located in the cerebral ganglion, the other in the left pedal ganglion.The present findings suggest the presence of a system of neurons that contain CDCH or CDCH-like peptides. The role this system may play in the control of egg-laying and egg-laying behaviour is discussed.     

Pedal neuron 3 serves a significant role in effecting turning during crawling by the marine slug <Emphasis Type="Italic">Tritonia diomedea</Emphasis> (Bergh)

The marine nudibranch Tritonia diomedea crawls using its ciliated foot surface as the sole means of propulsion. Turning while crawling involves raising a small portion of the lateral foot margin on the side of the turn. The cilia in the lifted area no longer contribute to propulsion, and this asymmetry in thrust turns the animal towards the lifted side. Neurons located in the pedal ganglia of the brain contribute to these foot margin contractions. T. diomedea has a natural tendency to turn upstream (rheotaxis), and pedal flexion neuron Pedal 3 elicits foot margin lift and receives modulatory input from flow receptors. To assess the contribution of this single cell in turning behavior, two fine wires were glued to the surface of the brain over left and right Pedal 3. We determined that Pedal 3 activity is correlated with subsequent ipsilateral turns, preceding the lift of the foot margin and the change in orientation by a consistent interval. Both Pedal 3 cells show synchronous bursts of activity, and the firing frequency of the ipsilateral Pedal 3 increased before turns were observed to that side. Stimulation of the electrode over Pedal 3 proved sufficient to elicit an ipsilateral turn in Tritonia.     

Ontogenesis of the snail,Helix aspersa: Embryogenesis timetable and ontogenesis of GABA-like immunoreactive neurons in the central nervous system

Late stages of embryogenesis in the terrestrial snail Helix aspersa L. were studied and a developmental timetable was produced. The distribution of gamma-aminobutyric acid-like immunoreactive (GABA-ir) elements in the CNS of the snail was studied from embryos to adulthood in wholemounts. In adults, approximately 226 GABA-ir neurons were located in the buccal, cerebral and pedal ganglia. The population of GABA-ir cells included four pairs of buccal neurons, three neuronal clusters in the pedal ganglia, two clusters and six single neurons in the cerebral ganglia. GABA-ir fibers were observed in all ganglia and in some nerves. The first detected pair of GABA-ir cells in the embryos appeared in the buccal ganglia at about 63–64% of embryonic development. Five pairs of GABA-ir cell bodies were observed in the cerebral ganglia at about 64–65% of development. During the following 30% of development three more pairs of GABA-ir neurons were detected in the buccal ganglia and over fifteen cells were detected in each cerebral ganglion. At the stage of 70% of development, the first pair of GABA-ir neurons was found in the pedal ganglia. In the suboesophageal ganglion complex, GABA-ir fibers were first detected at about 90% of embryonic development. In the posthatching period, the quantity of GABA-ir neurons reached the adult status in four days in the cerebral ganglia, and in three weeks in the pedal ganglia. In juveniles, transient expression of GABA was found in the pedal ganglia (fourth cluster).     

Neuroethology of Melibe leonina Swimming Behavior

The nudibranch Melibe leonina swims by rhythmically flexingits body from side to side at a frequency of 1 cycle every 2–5sec. Melibe swim spontaneously, when they are dislodged fromthe substrate, or when they come in contact with predatory seastars,such as Pycnopodia helianthoides. Intracellular recordings obtainedfrom semi-intact swimming Melibe reveal a population of 15 swimmotoneurons (SMNs) in each pedal ganglion. In general, SMNsin one pedal ganglion fire out-of-phase with SMNs in the oppositepedal ganglion, resulting in rhythmic side-to-side bending movements.In isolated brains, recordings from SMNs yield similar results,indicating the existence of a swim central pattern generator(CPG). There is no evidence for synaptic interactions betweenSMNs and either inhibiting or exciting SMNs has no impact onthe swim pattern. The SMNs are driven by a CPG consisting of4 interneurons; 2 in the cerebropleural ganglia and 1 in eachpedal ganglion. Appropriate bursting activity in the swim interneuronsis necessary for swimming to occur. Either hyperpolarizationor depolarization of any of the 4 CPG interneurons disruptsthe normal swim pattern. Swimming behavior, and the fictiveswim motor program expressed by the isolated brain, are inhibitedby light and nitric oxide donors. NADPH-diaphorase stainingand nitric oxide synthase (NOS) immunocytochemistry of Melibebrains suggests the source of nitric oxide might be a pair ofbilaterally symmetrical cells located in the cerebropleuralganglia.     

Coexistence of FMRFamide, met-enkephalin and serotonin in molluscan neurons

1. Coexistence of FMRFamide, met-enkephalin and serotonin immunoreactivities was examined in Achatina fulica and Aplysia kurodai. 2. Coexistence of FMRFamide and serotonin was found in some neurons of the visceral, right parietal and pedal ganglia of Achatina fulica, and in the pedal ganglion of Aplysia kurodai. 3. In Achatina fulica, coexistence of FMRFamide and met-enkephalin was found in a neuron of the left parietal ganglion and that of met-enkephalin and serotonin was found in a giant neuron of the right parietal ganglion. 4. Based on these results, the biological significance of coexistence was discussed.     

Serotonin-like immunoreactivity in the central and peripheral nervous systems of the interstitial acochlidean Asperspina sp. (Opisthobranchia)

Species of Acochlidea are common members of the marine interstitial environment and defined in part by their minuscule size and highly divergent morphology relative to other benthic opisthobranchs. Despite these differences, acochlideans such as species of Asperspina display many plesiomorphic characteristics, including an unfused condition of their neural ganglia. To gain insight into the distribution of specific neural subsets within acochlidean ganglia, a species of Asperspina was studied by using anti-serotonin immunohistochemistry and epifluorescence and confocal laser scanning microscopy. Results reveal similarities between Asperspina and larger opisthobranchs in the general distribution of serotonergic perikarya in the central nervous system. Specifically, the arrangement of perikarya into regional clusters within the cerebral and pedal ganglia and the absence of immunoreactive perikarya in the pleural ganglia are similar to the model species of Aplysia californica, Pleurobranchaea californica, and Tritonia diomedea. Moreover, serotonergic innervation of the rhinophores in all opisthobranchs, including Asperspina sp., originates from the cerebral ganglion instead of directly from the rhinophoral ganglion. Serotonergic innervation of the body wall, including the epithelium, muscles, and pedal sole, appears to arise exclusively from pedal and accessory ganglia. These observations indicate a general conservation of serotonin-like immunoreactivity in the central and peripheral nervous systems of acochlidean and other benthic opisthobranchs.     

Serotonin immunoreactivity of neurons in the gastropod Aplysia californica

Serotonergic neurons and axons were mapped in the central ganglia of Aplysia californica using antiserotonin antibody on intact ganglia and on serial sections. Immunoreactive axons and processes were present in all ganglia and nerves, and distinct somata were detected in all ganglia except the buccal and pleural ganglia. The cells stained included known serotonergic neurons: the giant cerebral neurons and the RB cells of the abdominal ganglion. The area of the abdominal ganglion where interneurons are located which produce facilitation during the gill withdrawal reflex was carefully examined for antiserotonin immunoreactive neurons. None were found, but two bilaterally symmetric pairs of immunoreactive axons were identified which descend from the contralateral cerebral or pedal ganglion to abdominal ganglion. Because of the continuous proximity of this pair of axons, they could be recognized and traced into the abdominal ganglion neuropil in each preparation. If serotonin is a facilitating transmitter in the abdominal ganglion, these and other antiserotonin immunoreactive axons in the pleuroabdominal connectives may be implicated in this facilitation.     

Qualitative and quantitative insights into the 3D microanatomy of the nervous ganglia of Scrobicularia plana (Bivalvia: Tellinoidea: Semelidae)

The nervous system of bivalves is bilaterally symmetrical and consists of interconnected cerebropleural, pedal and visceral ganglia, which may be partially to totally fused. We studied the microanatomy of the ganglia of Scrobicularia plana using three-dimensional (3D) reconstruction. We also examined whether intersex differences in the neural structure exist. Each type of ganglion had a characteristic 3D shape, and the cerebropleural ganglia shape was slightly asymmetrical. The visceral, pedal and cerebropleural ganglia are progressively smaller in volume, but only the pedal ganglion volume was positively correlated with the animal’s length, height or width; suggesting functional implications. As to total surface area, correlations were found for the cerebropleural and visceral ganglia, but it was the visceral that consistently showed strong positive correlations with each biometric parameter. The medulla may often penetrate the cortex and touch the capsule in areas that (contrary to what might be expected) are not connected with emerging nerves. Despite the differences in volume and surface area among ganglia, the volume ratio of cortex/medulla is fairly stable (c. 1.5), suggesting a functional optimum. Finally, we conclude that the ganglia of males and females do not show significant quantitative differences.