Acta Zoologica

Rao, Kotapalli Setha; Bushnell, John Horace

doi: 10.1111/j.1463-6395.1979.tb00605.xpmid: N/A

With the critical point drying method a scanning electron microscopic study of freshwater Ectoproct dormant structures was made. The suture zones of major phylactolaemate genera were described suggesting methods of their classification. The new structures revealed, throw light on the binding mechanism and early kinetics of germination of these dormant bodies. Median ribs and lateral ribs were described in the suture zones of Plumatella fruticosa, P. casmiana and Pectinatella magnifica. Dormant bodies of Fredericella sultana lack a medial or lateral rib in their suture zone. The fine structure of the polymorphic statoblasts of P. casmiana revealed different binding mechanisms as suited to different seasons. During germination, the internal pressure increases within the statoblast and the well cemented medial rib unfolds, letting its two valves separate. The mechanics of valve separations and subsequent germination were related to their respective environmental conditions favouring their domination.

Fänge, Ragnar

doi: 10.1111/j.1463-6395.1979.tb00606.xpmid: N/A

Parasitic protozoans, identified as Haemogregarina aeglefini (Henry), were found in erythrocytes of two gadiform fish, Melanogrammus aeglefinus (haddock) and Gaidropsaurus cimbrius (four‐bearded rockling). The latter species also harboured trypanosomes in its blood plasma, and a kind of intracellular parasite‐like inclusions in macrophages of the spleen, the pronephros and the liver. Most specimens of Gaidropsaurus cimbrius had leeches (Callobdella nodulifera) attached to the skin. A remarkable abundance of blood leucocytes noted in Gaidropsaurus cimbrius may be a response to haematozoan infections.

Reuter, Maria; Lindroos, Paula

doi: 10.1111/j.1463-6395.1979.tb00607.xpmid: N/A

The fine structure of the nerve cells in the brain of Gyratrix hermaphroditus is studied as well as the structure of the neuropile. General features of all nerve cells are a prominent neucleus with a small nucleolus, a scanty layer of cytoplasm containing mitochondria, free ribosomes, few profiles of granular endoplasmic reticulum, smooth endoplasmic reticulum, subsurface cisternae, well developed Golgi complexes, multivesicular bodies and numerous vesicles diagnostic for different nerve cell types. On the basis of the vesicle content four nerve cell types can be distinguished. The following types of vesicles are observed. Dense cored vesicles (50–80 nm), dense vesicles (60–120 nm), small lucent (synaptic) vesicles (40–50 nm), large lucent vesicles (50–200 nm) and lysosome‐like vesicles (200–500 nm). The significance of the variations in the interior electron dense material of the multivesicular bodies is discussed.

Reuter, Maria; Lindroos, Paula

doi: 10.1111/j.1463-6395.1979.tb00608.xpmid: N/A

The peripheral nervous system and the synapses of G. hermaphroditus are studied with the electron microscope. There is a submuscular as well as a subepithelial plexus. The subepithelial plexus is found among the muscles and between the muscles and the basement membrane. It consists of fibres containing large lucent and lysosome‐like vesicles and fibres with only small lucent (synaptic) vesicles. In the deeper lying submuscular plexus also dense and dense‐cored vesicles occur in the fibres. Cell bodies are not observed in the plexuses. The separate nerve supplies of the pharynx and the gonads contain nerve cells of the neurosecretory type. Fibres of the same kinds as in the brain are also seen here. The synapses in the neuropile are of two kinds. 1. Symmetrical synapses with an additional presynaptic network are most common. 2. Synapses without thickenings of membranes are observed between lateral membranes of neurites. In the peripheral nervous system are two other kinds of synapses also observed. 1. Asymmertical synapses with a denser and wider postsynaptic thickening and 2. neuromuscular junctions. Neurites containing accumulations of small vesicles against the basement membrane are also described. The organization of the peripheral nervous system is described and discussed in relation to the systematic position of G. hermaphroditus.

Saint‐Aubain, M. L.; Wingstrand, K. G.

doi: 10.1111/j.1463-6395.1979.tb00609.xpmid: N/A

A sphincter is described in the a. pulmonalis in the frog Rana temporaria. The sphincter begins abruptly where the pulmonary artery branches off from the a. pulmo‐cutanea. It is constricted by vagal stimulation and acetylcholine. It also contracts actively when the lungs are artificially collapsed and opens when the lungs are inflated. It is suggested that previously reported fibers in the vagus nerve, which come from stretch receptors in the lungs, act as the afferent reflex arch. When the pulmonary artery constricts, the cutaneous artery and vein are distended by increased pressure which contributes to increased cutaneous flow. The sphincter therefore seems to play an important role in the adjustment of circulation to exclusive cutaneous respiration as for instance in submerged, wintering frogs. It is suggested that the decrease of pulmonary flow in such situations causes increased mixing in the heart and, perhaps, complete break‐down of the double circulation. In frogs with exclusive skin respiration this would seem to be a functional necessity. Sphincters of similar location in turtles seem to be homologous with the one in Rana.

Zeiske, Eckart; Breucker, Haide; Melinkat, Reinhard

doi: 10.1111/j.1463-6395.1979.tb00610.xpmid: N/A

The olfactory organs of 6 rainbow fish species were studied, and were compared with those of closely related cyprinodonts. It has been found that, in contrast to cyprinodonts, the olfactory mucosa of rainbow fish is more conspicuously thrown up into folds. Their arrangement in parallel is considered a relatively primitive character of the organ. Electron microscopic investigations on Nematocentris maccullochi have shown that the sensory epithelium consists of basal, supporting, and two types of receptor cells, ciliated and microvillous. As in cyprinodonts the receptor cell cilia exhibit a basic 9 + 0 microtubular pattern. In Nematocentris the frequency of receptor cells, between 200,000 and 250,000 per mm2, is lower than in cyprinodonts. It may be suggested that the lower density is compensated for by enlargement of the sensory area due to the folding. In addition to broad‐surfaced dendritic membrane appositions found in both Nematocentris and cyprinodonts, contacts by means of dendritic spines are found only in the rainbow fish. The olfactory supporting cells of the latter are distinguished from those in cyprinodonts by more prominent lateral interdigitations, centrioles, and the higher number of vesicles associated with extensive Golgi complexes.

Obermüller‐Wilén, Helena

doi: 10.1111/j.1463-6395.1979.tb00611.xpmid: N/A

Ultrastructural and histochemical studies indicate a neurosecretory system exists in the lancelet brain with basal properties resembling a primitive hypothalamic system. A nucleus of secreting neurons, containing peptide granules (115 nm), is prominent in the dorsal walls of the brain. The axons establish contacts with the ventral brain surface, probably releasing their secretory product out of the brain. The neurons are innervated by dopaminergic “boutons en passant” often very active with a high number of electron translucent vesicles as well as dense‐core vesicles (90 nm). Ventrally located cellbodies containing what are probably secretory peptide granules (110 nm) establish contacts with their basal processes on the ventral brain surface.