THE FINE STRUCTURE OF DIFFERENTIATING SPERMATOZOA AND SERTOLI CELLS IN THE GONAD OF THE POND SNAIL, LYMNAEA STAGNALIS

The fine structure has been examined, of spermatogonia, spermatocytes,early spermatids, late spermatids and early spermatozoa nestlingagainst Sertoli cells in the gonad of Lymnaea stagnalis. Changes in the Sertoli cells are linked with the phases of spermdifferentiation. Details on differentiation particularly ofthe head of the sperm, are presented. (Received 14 March 1981;     

THE ULTRASTRUCTURE OF CILIATED CELLS FROM THE SIPHON OF SOLEN CAPENSIS (MOLLUSCA, BIVALVIA)

The structure of ciliated cells from the siphon of Solen capensishas been studied by both scanning and transmission electronmicroscopy. Two types of ciliated cell, based on the numberand length of cilia have been described which resemble thosedescribed in Donax. Type I is characterized by having 26–57({macron}= 43, n = 50) cilia which are 2.5 µm in length;Type II has fewer cilia (5–10; {macron}= 7) which are5 µn long. Both are primary receptors. Estimations ofabundance show that receptors are most numerous on the tipsof the siphon tentacles (8.8 x 10³/mm²). (Received 15 January 1985;     

SYNCHRONIZATION OF BACTERIAL CULTURE BY PREINCUBATION OF CELLS AT HIGH CELL DENSITY

The growth of Escherichia coli strain B in a liquid medium wasfound to cease at a cell density of 5x10⁹ cells per ml. (Thiscritical concentration is designated as the maximum or M-concentration.)Even cells harvested from the logarithmic growth phase couldnot divide at this or higher cell densities. Investigationson the metabolic activities of such cultures, however, showedthat the synthesis of cellular protein and nucleic acid wastaking place under such circumstances, showing that only someprocess (or processes) particularly related to cell divisionwas suppressed at the critical cell concentration in question. This finding led us to devise a new method of synchronizationof E. coli: cells harvested from a logarithmic phase were preincubatedat the critical concentration of 5x10⁹ cells per ml for 45 minutes,and then diluted 100 times with fresh medium. This led to synchronizationof cell division, as shown by a stepwise multiplication in cellnumber. (Received June 20, 1961; )     

RIBONUCLEIC ACIDS APPEARING DURING THE PROCESS OF CHLOROPLAST REGENERATION IN THE "GLUCOSE-BLEACHED" CELLS OF CHLORELLA PROTOTHECOIDES

1. Investigations were made on the modes of synthesis of differentspecies of RNA which appear during the greening (chloroplastregeneration) of the "glucose-bleached" cells of Chlorella protothecoidescontaining profoundly degenerated plastids.
2. RNAs were extractedfrom the algal cells which had been labelledwith ³²P for 1hr before harvesting at different stages of thegreening inthe light and in darkness, and subjected to columnchromatographywith methylated albumin-coated kieselguhr. Itwas found that,during the greening process, the elution profilesof RNAs, interms of the optical density at 260 mµ and³²P-radioactivity,changed profoundly.
3. Based on these and other results, it wasconcluded that duringan early phase of the chloroplast regenerationin the glucosebleachedalgal cells, there occurs an active formationof both ribosomalRNAs (rRNAs) and the RNAs corresponding tosoluble RNA (sRNA),the formation coming, however, later toa standstill when thesynthesis of chlorophyll has proceededto a certain level. Thequantity ratio of sRNA to rRNA was foundto be constant (30:70)at different stages of the greening (bothin the light and indarkness), with a few exceptions. The synthesisof the chloroplastribosomal RNA is markedly accelerated bylight, and its maximumrate is observed sometime later thanthat of the non-chloroplast("cytoplasmic") ribosomal RNA. Itwas suggested that there areat least two different sites ofsynthesis of ribosomal RNAs,one in the plastid and the otheroutside of it (most probablyin the nucleus).

¹A part of this work was reported at the Symposium on Cell Differentiationsponsored by the Institute of Applied Microbiology, Universityof Tokyo, in November 1965. ² Present address: Institute for Plant Virus Research, Ministryof Agriculture and Forestry, Aoba-cho, Chiba.     

DEGRADATION AND FORMATION OF SULFOLIPID OCCURRING CONCURRENTLY WITH DE- AND RE-GENERATION OF CHLOROPLASTS IN THE CELLS OF CHLORELLA PROTOTHECOIDES

1. It has been demonstrated that when the cells of Chlorella protothecoidesare grown mixotrophically under illumination in a medium richin nitrogen source (urea) and poor in glucose, the normal greencells are obtained, while in a medium rich in glucose and poorin the nitrogen source, entirely chlorophyll-less cells withprofoundly degenerated plastids ("glucose-bleached" cells) areproduced, irrespective of whether in the light or in darkness.The "glucose-bleached" cells turn green with regeneration offully organized chloroplasts when incubated in a nitrogen-enrichedmedium in the light ("light-greening"), while in the dark theybecome pale green with formation of only partially organizedchloroplasts ("dark-greening"). When, on the other hand, thegreen cells are transferred into a medium enriched with glucose,they are bleached fairly rapidly with degeneration of chloro-plastsin the light as well as in darkness ("bleaching"). Using ³⁵Sas a tracer, investigations were made on the changes of contentsof the algal cells in sulfolipid and other sulfur compoundsduring the processes of the greening and bleaching.
2. By determiningthe radioactivities of chromatographically separatedsulfur-containingcompounds of the uniformly ³⁵S-labeled green("G") and "glucose-bleached"("W") cells, it was found thatthe concentration of a speciesof sulfolipid (discovered byBENSON et al.) as well as thoseof glutathione, sulfotriosesand most of the other sulfur-containingcompounds were at least5 times higher in the "G" cells thanin the "W" cells, whilesulfoquinovosyl glycerol was presentin approximately equalamounts in the two types of cells.
3. Phospholipidcontents and compositions in the two types of algalcells werefound to be practically identical.
4. The sulfolipid contentof algal cells increased and decreasedalmost in parallel withthe processes of greening and bleaching,respectively.
5. Studyingthe mode of incorporation of radiosulfate into varioussulfurcompounds of algal cells during the processes of "light-anddark-greening" and "bleaching" (lasting about 70 hr), itwasfound that active ³⁵S-incorporation into sulfolipid occurredthroughout the process of "light-greening," while in the "dark-greening"and "bleaching" the active incorporation abruptly ceased afterthe initial 24 hr period of experiments. It was suggested thatthe biosynthesis of the sulfolipid is closely related to theformation of photosynthetic apparatus in chloroplast.
6. Whenthe ³⁵S-labeled green cells were bleached in a medium containingno radiosulfate, the ³⁵S-sulfolipid and most of other ³⁵S-sulfurcompounds decreased markedly but the ³⁵S-sulfoquinovosyl glycerolincreased considerably. It was inferred that the deacylationof the sulfolipid, a surfactant lipid, with formation of watersoluble sulfoquinovosyl glycerol may be a cardinal event ofbleaching process, causing a disintegration of the intact architechtureof photosynthetic apparatus.
7. Based on these observations itwas concluded that the sulfolipidis an integral component ofphotosynthetic structure.

¹This work was partly reported at the Symposium on Biochemistryof Lipids, sponsored by the Agricultural Chemical Society ofJapan, Sapporo, July, 1964.     

THE FINE STRUCTURE AND FUNCTION OF THE ANAL GLAND OF THE MURICID NUCELLA LAPILLUS (NEOGASTROPODA) (AND A COMPARISON WITH THAT OF THE TROCHID GIBBULA CINERARIA)

The fine structure of the anal gland of Nucella lapillus isdescribed, and compared with that of Gibbula cineraria. It isconcluded that the glands are not analogous in function andare unlikely to be homologous. The anal gland of Gibbula isa small rectal diverticu-lum near the anal papilla, lined bymucus-secreting cells. The evidence suggests that the largeanal gland of Nucella extracts macromolecules and cations fromthe blood, metabolizes or sequesters them in lyso-somes andultimately expels the resultant residual bodies by apocrinesecretion. It has large reserves of lipid and glycogen, andthe abundance of melanin indicates that it is a major site oftyrosine degradation. The invariable presence of bacteria inthe lumen, and of pits in the epithelium to house them, impliesa symbiotic relationship in which the bacteria metabolize anddegrade the cell debris, some of which is resorbed. The lossof the anal gland in bucci-nids and nassariids is accompaniedby great reduction in size and importance of the rectal sinus,and increase in complexity of the kidney. (Received 31 December 1991; accepted 23 January 1992)     

THE MORPHOLOGY, ULTRASTRUCTURE AND FUNCTION OF THE FEEDING APPARATUS OF SAYELLA FUSCA (C.B. ADAMS, 1839) (GASTROPODA: PYRAMIDELLIDAE)

Scanning and transmission electron microscopy in conjunctionwith histology and dissection were employed to investigate theforegut anatomy of Sayella fusca (C.B. Adams, 1839), a commonNew England pyramidellid snail. Certain aspects of the feedingapparatus of S. fusca, including the buccal pump and proboscisanatomy, depart from the characteristic pyramidellid plan. Somedifferences such as the position of the introvert/proboscisaperture and the common oral and stylet canal are shared withthe genera Turbonilla, Eulimella, and Pyramidella. Three characteristicsof the feeding apparatus are unique to S. fusca: (1) the buccalpump is not divided into two pouches but exists as a singlemuscular bulb; (2) the entire lumen of the buccal pump, notsimply a portion of it, possesses a cuticular lining; and (3)the salivary ducts never enter the muscular walls of the buccalpump. Histological studies of the salivary gland indicate thatthree types of secretory cells are intermittently distributedthroughout the entire gland rather than characterizing distinctregions as described for other members of the family Pyra-midellidae.In contrast to previous findings, the gland cells of S. fuscaexhibit a merocrine secretion. The taxonomic value of the buccalpump and proboscis morphology are discussed. ^*Present address: Dauphin Island Sea Lab, 101 Bienville Boulevard,Post Office Box 369–370, Dauphin Island, Alabama 36528USA. (Received 9 November 1993; accepted 1 October 1997)     

DYNAMIC RESPONSE OF ROOT BORDER CELLS AND THEIR ASSOCIATED MUCILAGE EXUDATION IN SOYBEAN TO AI STRESS AND RECOVERY

 以耐铝性明显差异的两个大豆(Glycine max)基因型‘浙秋2号’(耐性)和‘浙春3号’(敏感)为材料, 研究根尖边缘细胞比活度、粘液分泌和根长对铝胁迫和解除胁迫的反应, 明确边缘细胞的粘液分泌对策在铝毒环境中的生态学意义。结果表明, ‘浙秋2号’在100~400 µmol&;#8226;L^–1 Al³⁺处理的3~12 h, 边缘细胞比活率呈递减趋势, 12 h后比活率又略有上升。‘浙春3号’在300和400 µmol&;#8226;L^–1 Al³⁺处理的变化与前者一致。两个大豆基因型的粘液层随着Al³⁺浓度增加和时间延长而增厚, 并于400 µmol&;#8226;L^–1 Al³⁺处理24 h时达到最大(>17 µm)。‘浙秋2号’在低浓度Al3+ (100和200 µmol&;#8226;L^–1)处理3~6 h后就会分泌大量粘液, ‘浙春3号’则在300 µmol&;#8226;L^–1 Al³⁺处理12 h后才有类似的变化。‘浙秋2号’在400 µmol&;#8226;L^–1 Al³⁺处理下的根相对伸长率均高于100~300 µmol&;#8226;L^–1 Al³⁺处理, ‘浙春3号’则表现为Al³⁺浓度越高, 根伸长受抑越明显。Al³⁺胁迫解除后, ‘浙秋2号’的粘液分泌速度和分泌量急剧下降, ‘浙春3号’在胁迫解除后的24 h, 仍会持续、大量地分泌粘液(>19 µm)。可见, 耐性大豆通过在铝胁迫初期快速、大量地分泌粘液以维持较高的边缘细胞活性和解除胁迫后迅速降低粘液的分泌速度及分泌量来适应铝毒害环境。     

THE FINE STRUCTURE AND FUNCTION OF THE SALIVARY GLANDS OF NUCELLA LAPILLUS (GASTROPODA: MURICIDAE)

The fine structure of the tubular and acinous salivary glandsof Nucella lapillus (L.) has been studied and some histochemicaland enzyme tests have been carried out. The clusters of subepithelialcells of the tubular glands secrete a glycoprotein composedof chains of tubular macromolecules resembling secretions knownto have adhesive properties which may assist in boring. Thesecretion is rich in disulphide groups, as are many toxins,and is believed to be responsible for the recently demonstratedpharmacological activity of the glands. It is proposed thatflaccid paralysis is induced in prey by envenomation with thissecretion during rasping, after soft parts have been exposedby an ‘anti-predator’ reaction to secretion fromthe hypobranchial gland of Nucella. The secretory vesicles ofboth types of gland cells in the acinous glands have heterogeneouscontents indicating that their secretions are complex. The majorcomponent in those of the mucous cells is an acid mucopolysaccharidetypical of a lubricant or releasing agent. The ciliated basalcells resemble typical enzyme-secreting cells and the majorconstituent of their secretion is a finely granular glycoprotein. (Received 8 January 1990; accepted 5 June 1990)     

REABSORPTION OF ORGANIC SOLUTES IN SOME MARINE AND FRESHWATER PROSOBRANCH GASTROPODS

Influx in vitro of glucose to the heart, kidney and ureter,where present, in Monodonta, Pomacea, and Viviparus, and alsoof leucine to these tissues in Viviparus, was measured using[³H]-labelledtracers. Phloridizin-sensitive, Na⁺-dependent [³H]D-glucose uptake wasevident in the papillary sac of Monodonta, the ventricle ofViviparus, and the kidney of Pomacea. Viviparus ventricle alsoshowed Na⁺-dependent uptake of [³H]L-leucine. Nevertheless Viviparusappears to excrete some amino acids (by undefined routes) andmay therefore lack the carriers for their resorption. In Viviparusand Pomacea the site of organic solute resorption (taken tobe where Na⁺-dependent tracer uptake predominates) is proximalto the sites of Na⁺resorption. The ultrastructure of the resorptivesites has been examined in the three genera and compared withthat of the nephridial gland and dorsal wall of the kidney ofLittorina. The ciliated cells comprising the epithelium of thepapillary sac in Monodonta and their homologues over the nephridialgland and dorsal wall of Littorina and dorsal wall of Pomaceashow common features typical of transporting epithelia in othermolluscs. The ventricular epicardium of Viviparus shows secondaryspecializations for resorption but lacks an endocytotic canalsystem. The site of organic solute resorption (the most highlyspecialized part of which is the nephridial gland in marinespecies), has been correlated with the anatomy of the renalveins in the four genera, and with other specializations inthe freshwater genera.The difficulty of quantifying rates oftransport of solutes from studies in vitro is discussed. ^*Present address: Dept. of Physiology, The University, DundeeDD1 4HN (Received 31 January 1989; accepted 24 March 1989)     

EFFECTS OF WOUND HEALING ON ZINC DISTRIBUTION AND ALKALINE PHOSPHATASE ACTIVITY OF HELIX ASPERSA (GASTROPODA: PULMONATA)

Helix aspersa were loaded with ⁶⁵zinc and after 2 and 5 daysstarvation there was no significant reduction in the zinc concentrationof the digestive gland and shell. Wounding of the optic tentacle,foot tissue and partial shell removal of H. aspersa resultedin deposition of ⁶⁵zinc in the wound area. Alkaline phosphataseshowed no increase in concentration at the sites of wounding. (Received 15 October 1985;     

DISTRIBUTION AND TURNOVER OF PHOSPHATE COMPOUNDS IN GROWING CHLORELLA CELLS

1. Using the Chlorella cells which had been uniformly labeled with³²P, the distribution of phosphorus in various fractions ofcell material was investigated. Uniformly ³²P-labeled Chlorellawas further grown in a P-free medium or in a standard "cold"medium, and the change of distribution of ³²P (as well as theuptake of exogenous P) in various cell fractions was followed.
2. Analysis of the ³²P-labeled algal cells showed that the highestin P-content was the fraction of RNA followed by those of polyphosphates,lipid, nucleotidic labile phosphate compounds, DNA and protein(in decreasing order). ATP and ADP were found to be only minorfractions of the total labile phosphates.
3. On incubating the³P-labeled alga in a P-free medium, the P.contentsin the fractionsof DNA, protein, lipid and ATP increased, thosein polyphosphatesand ADP decreased, and that in RNA remainedalmost unchanged.When the ³²P-labeled alga was further grownin the normal "cold"medium, DNA and protein increased withthe expenditure of endogenous³²P, but with practically no incorporationof external P. Inthe meantime the P in polyphosphates decreasedconsiderably,and the RNA fraction incorporated a large amountof externalP but only a little of endogenous³²P.
4. It was inferred that,under the experimental conditions of thepresent study, thephosphorus used in the syntheses of DNA andprotein was primarilytaken from polyphosphates, while thatused in the synthesesof RNA, phospholipid and polyphosphateswas, for the most part,taken from the extracellular P-source.

¹A part of this paper was read at the Vth International Congressof Biochemistry, Moscow, August 10–16, 1961. (Received June 4, 1961; )     

Studies on the Growth in Culture of Plant Cells: XXIII ISOLATION OF NUCLEI AND HISTONES FROM CULTURED CELLS OF ACER PSEUDOPLATANUS L.

A technique is described for the isolation of purified nucleifrom suspension culture cells of Acer pseudoplatanus. This involvesa grinding medium containing 70% (v/v) glycerol, 1 mM Mg²⁺,2 mM Ca²⁺, and Tris buffer at pH 7.8, prestorage and disruptionof the cells at –20 °C in a Potter-Elvehjem homogenizer,and purification by filtration and centrifugation in the presenceof Triton X-100. The nuclear yield is c. 25% as assessed bynuclear count or DNA estimation and the nuclei are active inthe RNA synthesizing system of Tautvydas (1971). When the histones of these nuclei are extracted in H₂SO₄ andprecipitated by ethanol, 113 µg histone is obtained perµg nuclear DNA and the histone fraction contains 22% basicamino acids and has a lysine: arginine ratio of 2.6. Acid-ureagel electrophoresis shows the presence of five major histones(H1, H2A, H2B, H3, and H4 in sequence from anode to cathode)having respectively molecular weights of 24 500, 13 500, 13300, 12 800, and 11 000. There is very good correspondence betweencalf thymus histones H3 (reduced form) and H4 and two of theseAcer histones. The other Acer histones differ from the calfthymus histones H1, H2A, H2B in molecular weight but can beprovisionally equated with these by a newly developed differentialstaining reaction. Calf thymus histone H2A appears to be lessrich in lysine than the corresponding Acer histone. Evidence from a pulse-chase experiment with (¹⁴C)lysine and[³H]tryptophan is in favour of the cytoplasmic synthesis ofthe histones.     

QUANTITATIVE SEPARATION OF INORGANIC POLYPHOSPHATES IN CHLORELLA CELLS

Using unicellular green alga, Chlorella ellipsoidea, which hadbeen labeled with ³²P-phosphate, re-examination was performedon our routine method for the quantitative separation of inorganicpolyphosphates (poly-Pi). Confirming the previous results, itwas demonstrated that poly-Pi's in Chlorella cells are clearlyseparated from each other by successive extractions with cold8% TCA (poly-Pi "A"), with cold KOH at pH 9 (poly-Pi "B"), andwith 2 N KOH (poly-Pi's "C" and "D"; the former precipitateson neutralization with PCA, leaving the latter in solution).Use of 2N KOH was found to be most suitable for the purposeof fractionation of poly-Pi's "C" and "D." (Received February 25, 1965; )     

PERMANGANATE FIXATION OF THE GOLGI COMPLEX AND OTHER CYTOPLASMIC STRUCTURES OF MAMMALIAN TESTES

Observations on the fine structure of KMnO₄-fixed testes of small mammals (guinea pig, rat, and mouse) reveal certain morphological differences between the spermatogenic and Sertoli cells which have not been demonstrated in the same tissue fixed with OsO₄. Aggregates of minute circular profiles, much smaller than the spherical Golgi vesicles, are described in close association with the Golgi complex of developing spermatids. Groups of dense flattened vesicles, individually surrounded by a membrane of different dimensions than that which bounds most of the other cell organelles, appear dispersed within the cytoplasm of some spermatogenic cells. Flattened vesicles of greater density than those belonging to the Golgi complex are reported confined to the inner Golgi zone of developing guinea pig spermatids between the Golgi cisternae and the head cap. The profiles of endoplasmic reticulum within spermatocytes appear shorter, wider, and more tortuous than those of Sertoli cells. Minute cytoplasmic particles approximately 300 A in diameter and of high electron opacity appear randomly disposed in some Sertoli cells. Groups of irregular-shaped ovoid bodies within the developing spermatids are described as resembling portions of cytoplasm from closely adjacent spermatids. Interpretation is presented regarding the fine structure of KMnO₄-fixed testes in view of what has already been reported for mammalian testes fixed in OsO₄.     

CATALYTIC EFFECTS OF CARBON DIOXIDE IN CARBON DIOXIDE ASSIMILATING CELLS

It has been confirmed that absence of carbon dioxide may decreasethe rate of oxygen production which accompanies the photochemicalreduction of p-benzoquinone in algae and chloroplasts. Thisinfluence of carbon dioxide partial pressure does not applyto the overall oxygen yield. In the blue-green alga Anacystisnidulans the initially small carbon dioxide deficiency effectincreases with time spent in the dark. The deterioration ofreaction rates is counteracted by light. There seems to be nodirect connection or interdependence between the photosyntheticreduction of carbon dioxide and the sensitivity of some partof the photochemical mechanism to loss of carbon dioxide. Notonly does addition of quinone to living cells in these experimentsdestroy their capacity for photosynthesis, but mutant cellsthat never had this capacity still retain the sensitivity towardslack of carbon dioxide when tested for their ability to reducequinone. Many different metabolic reactions have been seen topossess such dependency on traces of carbon dioxide, also innon-photosynthetic cells and tissues. The explanation for "catalytic"effects of carbon dioxide ought to be a general one–suchas an influence on the efficiency of certain phosphorylationswhich occur everywhere in the living world. ¹ Dedicated to Prof. H. TAMIYA on the occasion of his 60th birthday.These studies were aided by contract NONR 988 (10) between theOffice of Naval Research, Department of the Navy, and the FloridaState University, respectively. ² Present address: Charles F. KETTERING Research Laboratories,Yellow Springs, Ohio. (Received December 7, 1962; )     

Movements of K+ during Shutting and Opening of the Trap-Lobes in Aldrovanda vesiculosa

K⁺ movements during the shutting and subsequent opening of trap-lobesin Aldrovanda vesiculosa were measured using ⁸⁶Rb as a tracerfor K⁺. Immediately after the shutting, a large amount of ⁸⁶Rbpre-loaded in the trap-lobes was detected in the hollow spaceinside the shut trap. This may indicate that much of the K⁺in the active motor cells leaks out during the shutting, resultingin turgor loss in the cells. ⁸⁶Rb(K⁺) uptake in the trap wasactive. During the opening process, enhanced ⁸⁶Rb uptake wasobserved. The time course of this uptake was similar to thatof the opening of the trap-lobes, and both courses were acceleratedby IAA. Enhanced K⁺ uptake may restore the turgor in activemotor cells. The quantity of K⁺ that moved during the shuttingor opening was estimated as 20% of that in the active motorcells in the open state of the trap-lobes. The K⁺ efflux acrossthe membranes of the active motor cells may be caused by a largeincrease in bulk flow triggered by an action potential, andwas estimated as 6,200 pmol.cm^–2. ¹ This paper is dedicated to the memory of Professor Joji Ashidawho established the physiology of rapid movement in Aldrovandavesiculosa. (Received July 22, 1982; Accepted November 11, 1982)     

Transnodal Transport of 14C in Nitella flexilis: II. TANDEM CELLS WITH APPLIED PRESSURE GRADIENTS

Using carefully standardized test conditions and tandem pairsof cells of Nitella flexilis, the influx of ¹⁴C (added as H¹⁴CO₃^–and transnodal transport were studied under various pressuregradients applied across the node up to P=± 2·5bar. When mannitol was used as the osmoticum, influx was foundto increase only when the mannitol solution was around the cellproximal to the feed. ¹⁴C was transported across the node tothe distal cell, probably as ¹⁴C-photosynthate products, evenagainst a pressure gradient of 2 bars or more, as was ³⁶Cl^–and ³²P. The % transported in general decreased with increasingP, whether assisted or opposed by added pressure. It was unchangedby the presence of mannitol at the node and was essentiallythe same whether the pressure gradient was produced by directpressure or by use of the osmoticum. Transnodal transport of¹⁴C products is almost certainly via plasmodesmata and appearsto be largely by an active mechanism. In absolute amounts itis the same whether the pressure gradient assists or opposesflow. Valving is evident at the node, increasing the resistanceto transport as the pressure gradient increases whether ¹⁴C(asHCO₃^–), ⁴²K⁺ (as KCl), ³⁶Cl^– (as NaCl) or ³²P (asNa₃PO₄) are used to detect it. The mechanism of movement ofK⁺ across the node differs from that of photosynthate products. Key words: Node, plasmodesmata, pressure gradients, active transport     

PEDAL AND OPERCULAR SECRETORY GLANDS OF POMATIAS, BITHYNIA AND LITTORINA

The histochemical properties of the pedal and opercular glandcells of three prosobranchs from different habitats were examined.The suprapedal gland of Pomatias elegans contained 3 gland celltypes producing mucoprotein, protein and sulphated muco-polysaccharide.The ventral surfaces of the foot were devoid of gland cellsexcept in the median furrow in which two cell types producea neutral and a sulphated mucopolysacharide. The dorsal surfaceof the foot possesses 5 cell types which produce a variety ofmucosubstances. The anterior pedal gland of Bithynia tentaculata produces neutraland weakly acidic mucoprotein from one cell type. The ventralsurface of the foot is generally populated by gland cells oftwo types producing acid mucopolysaccharide and protein. A furthercell type producing carboxylated mucopolysaccharide is restrictedto a transverse band mid-way down the foot. The dorsal surfaceof the foot is covered by mucus from three cell types producinga variety of mucosubstances. The anterior pedal gland of Littorina littorea possesses twocell types both of which secrete mucoprotein. The ventral surfaceof the foot secretes sulphated and carboxylated mucopolysaccharideand a mucoprotein from three cell types which form a thick subepi-dermalglandular layer. The dorsal surface is lubricated by a sulphatedmucopolysaccharide and a mucoprotein. The secretory cells of the dorsal surface extend into the operculargroove and disc whose specialised cells generally secrete mucopolysaccharideand at least two differently staining proteins. ^*Present address: Department of Zoology, University of Durham,Durham City, U.K. (Received 19 August 1986;     

COMPARATIVE SPERMATOLOGY OF FOUR SYMPATRIC SPECIES OF SIPHONARIA (PULMONATA: BASOMMATOPHORA)

The fine structure of the modified sperm and spermatogenesisof four sympatric species of Siphonaria is described. The morphologyof the sperm of all species is very similar. The head, whichis about 6 µm long, is composed of a nucleus with fibrouschromatin capped by an acrosome (about 1 µm long) comprisedof an acrosomal pedestal and apical vesicle. The midpiece hasa mitochondrial derivative which surrounds a single glycogenhelix, posterior to which is a glycogen piece. Although differencesbetween each species exist, the value of sperm morphology forpurposes of taxonomy in this genus is questioned. Comparisonwith other basommatophorans however suggests that sperm morphologymay be of value at a higher taxo-nomic level. The morphologicalchanges that occur during spermatogenesis are similar to thosedescribed for other molluscs with modified sperm, except thatduring early spermiogenesis the Golgi body and smooth endoplasmicreticulum become highly developed. This proliferation of theSER and Golgi occurs at the same time as elongation of the spermatid.Throughout spermatogenesis, the germ cells are closely associatedwith a somatic cell which, because of structural similaritieswith the somatic cell of mammalian seminiferous epithelium,has been termed a Sertoli cell. After the spermatids have beenreleased from the Sertoli cells of the testis, maturation continuesin the hermaphrodite duct where the acrosome reaches its finalsize and glycogen accumulates in the glycogen compartment ofthe mid-piece. (Received 25 April 1990; accepted 1 September 1990)