The fate of an internal parasitoid,Nemeritis canescens,in a variety of insects

• 1 The fate of Nemeritis canescens has been studied in 36 species or, counting different stages, in 51 kinds of insects, in order to discover the causes of its success or failure in each.
• 2 The parasitoid was able to develop to the adult stage in 14 of the species studied.
• 3 A defence reaction of the host, cellular encapsulation, was by far the most frequent cause of the death of canescens in species in which it could not develop.
• 4 Deposition of melanin over its mouth probably caused the death of canescens in two species; in other species the role of melanisation was subordinate to encapsulation.
• 5 Very few species, if any, were unsuitable as food; larvae of the parasitoid ingested and assimilated the blood of a wide variety of insects.
• 6 Some individuals of a few species were unsuitable as a habitat for the parasitoid larva.
• 7 The survival of canescens in suitable hosts is discussed with reference to the means by which this parasitoid resists defence reactions.
• 8 Attention is drawn to incidental results of the research: (i) a state of diapause in some hosts was transmitted to first-instar larvae of canescens and delayed their development; (ii) evidence was found that the teratocytes formed by braconid parasitoids function as a means of preventing cellular defence reactions, that they act by attrition of the host, and that they protect a larva of canescens present in the same host; (iii) observations concerning the behaviour of adult canescens in attacking some species, and the survival of supernumerary larvae after competing for the host, are mentioned.

     

Relationship between Electrical Resistance and Capacitance of Wood in Progressive Stages of Discoloration and Decay

Electrical resistance and capacitance measurements were madeon woody tissues of several tree species. Each tissue was abovethe fibre-saturation point. Values of capacitance were inverselyproportional to values of resistance in woody tissues in progressivestages of discoloration and decay. With the electrode separationused, clear woody tissues had resistances of 110 to 30 k andcapacitances of 0·002 to 0·110 µF. Resistanceand capacitance measure ments of discoloured tissues were 29to 8 k and 0·005 to 0·040 µF, respectively,and those of decayed tissues were 5 to 1 k and 0·60 to0·110 µF. Either electrical measurement could beused to measure the stages of deterioration in woody tissues.Ground woody tissues, cellulose suspensions, starch suspensions,and wood equivalent solutions of potassium chloride had resistanceand capacitance properties similar to those found in intactwoody tissues. Electrical resistance and capacitance propertiesof woody tissues above the fibre-saturation point appear tobe similar to those of dilute solutions of mobile ions.     

Observations on the Ultrastructure of Uronema spp., Marine Scuticociliates*

SYNOPSIS. Observations of the ultrastructure of marine scuticociliatids, tentatively assigned to the genus Uronema, were made by light, transmission electron, and scanning electron microscopy. Giant, cortically oriented mitochondria filled the subpellicular, intermeridional areas, and were in close association with the epiplasm immediately under the inner alveolar sac membranes. Reconstructions of serial sections of the posterior poles of ciliates indicated that the intermeridional mitochondria could fuse at that point and the entire chondriome might at times be a single organelle. A system of tubules was observed to be intimately associated with the mitochondria in the posterior region. The tubules anastomosed and were directed posteriorly into the region of the nephridial-contractile vacuole system. The outer surfaces were coated with projections arranged in helical patterns. The system may be regarded as a fluid segregation organelle. The tripartite nature of the polar basal body complex observed by silver impregnation was confirmed by transmission electron microscopy. The 3 structures were the basal body of the caudal cilium and 2 parasomal sacs. A prominent ring around the caudal cilium was observed by scanning electron micrcscopy; it is probably responsible for the silver deposition surrounding the polar basal body complex that can be seen by light microscopy of silver-impregnated specimens. The ultrastructure of the nonmotile caudal cilium and its kinetosome was unremarkable, being like that of the motile, somatic cilia. The micronuclear and macronuclear outer membranes were continuous at several sites. Such interconnections explain the intimate physical relationship between the nuclei during interphase in many ciliates, and could be a structural basis for chemical communication between the 2 nuclear types. Within the cytoplasm surrounding the opening of the cytoproct, numerous clear vesicles were observed. Their position and appearance suggested that the cytoproct may be involved in the elimination of solutions as well as solids. Food vacuoles, cortical microtubules, lamellar vesicles, disc-shaped vesicles, mucocysts, and a contractile vacuole and its pore were also observed.     

Arginine Vasotocin: Structure-Activity Relationships and Influence on Gonadal Growth and Function

When AVT (arginine vasotocin) was given neonatally during theperiod when the brain is undergoing sexual differentiation,increased growth of the reproductive organs was observed inadulthood. Injection of AVT after this neonatal period in immatureanimals led to diminished growth of the accessory organs andin some cases the gonads themselves. The hypertrophic responseof the in situ ovary in adult mice following unilateral ovariectomy(UO) was inhibited in a dose-related manner by a single intraperitonealinjection of freshly prepared AVT. Much less AVT was requiredfor this response when injected into the third ventricle. Afterintraperitoneal injection, arginine vasopressin (AVP), lysinevasopressin (LVP), and 4-leucine vasotocin (4-leu-AVT) alsoinhibited compensatory ovarian hypertrophy whereas oxytocindid not. The commonality in die structure of these antigonadotrophicpeptides include a closed ring and a basic amino acid in position8. After opening the disulfide bond of these nonapeptides withmercaptoethanol, a single injection of the reduced AVT, AVP,LVP, or 4-leu-AVT into UO mice causes exaggerated hypertrophyof the remaining ovary. When added with leuteinizing hormone-releasinghormone (LRH) to culture medium containing hemipituitaries fromcastrated estrogen-progesterone primed female rats, AVT significantlyincreased the release of radioimmunoassayable LH above thatdue to LRH alone. AVT might interact at all levels of the hypothalamo-hypophysealgonadalaxis.     

Ribonucleoprotein-Containing Vesicles in Cysts of Naegleria gruberi*

SYNOPSIS. Ultraviolet microscopy and electron microscope autoradiography were used to study ribonucleoprotein in cysts of Naegleria gruberi. The absorption maximum for cysts is at 265 nm with little detectable absorption occurring at 295 nm. Pre-cystic trophozoites absorb less strongly than the cysts at 265 mm. Acridine orange staining indicated concentrations of ribose nucleic acid or ribonucleoprotein in the cytoplasm of young cysts. The dye stained discrete vesicles in the cytoplasm. Tritiated uridine and tritiated proline were used to follow changes in RN-protein at encystment. Label was incorporated into vesicles filled with ribosome-like particles. These are presumably the sites of acridine orange staining. Relatively little label was associated with the cyst cytoplasmic matrix; most of the silver grains lay over the nucleus and cytoplasmic organelles. The vesicles are believed to represent autophagosomal-type vacuoles with the contents derived from breakdown of organelles such as mitochondria. The path of label into the vesicles is via lysis of labeled cytoplasmic organelles. The RN-protein vesicles of Naegleria gruberi cysts are compared to the chromatoid bodies of Entamoeba invadens. It is concluded that, tho differences in detail are present, the role of the structures in the cysts is probably the same. They are a ready source of amino acids and ribosomes in a dedifferentiated or pool state to be used for synthetic reactions that accompany resumption of trophic existence.     

Induction of the Feline Oncornavirus Associated Cell Membrane Antigen in Human Cells

BY N-terminal amino-acid sequence analysis, Glenner et al.¹ have shown that amyloid fibrils are very similar to the variable part of an immunoglobulin kappa light chain (Bence-Jones protein Ker) and they suggested that amyloid is constituted by immunoglobulin light chains.     

The Relationship between Stimulus Intensity and Oriented Phototactic Response (Topotaxis) in Chlamydomonas

Two techniques have been used to study the quantitative relationship between stimulus intensity and oriented phototactic response (topotaxis) in Chlamydomonas. The net response of a cell population was monitored photometrically and was recorded continuously against time. The responses of individual cells were observed through a microscope and their swimming tracks were recorded on film. The net response of the population is positive at low stimulus intensity and negative at high intensity. The direction of response can be reversed within two seconds by raising or lowering the intensity. The intensity-response curve for phototaxis is similar to the dose-response curve for phototropism. The net response has no distinct threshold; it increases linearly with log intensity; then it decreases and finally becomes negative. The individual-cell studies reveal that the intensity-dependent increase in net topotactic response is due primarily to an increase in the number of cells responding and in the directness of their swimming path. As stimulus intensity is raised, the swimming path becomes increasingly well-aligned with the stimulus beam, whether net response is positive throughout the intensity range tested, negative throughout that range, or changing from positive to negative. Changes in swimming rate do not contribute significantly to the intensity-dependent changes in net response. Swimming rate shows virtually no change throughout the intensity range of positive topotaxis and shows only a small increase in the negative range. However, a transient decrease in swimming rate (stop response) is often observed at the onset of stimulation. The implications of these results for the orientation mechanism are discussed.