摘要:

AbstractArterio‐venous association was investigated in the tibial region of 66 bird species representing 21 orders. An intermingled network of arteries and veins (rete tibiotarsale) was found in all stages of complication, ranging from the most simple with only 3 arteries and 5–7 veins (tinamou and owl) to the most elaborate types with more than 60 arteries and 40 veins (flamingo). As opposed to what has hitherto been believed, elaborate retia are present in many short‐legged species, while most of the long‐legged wading birds only have retia of a very simple type. Arctic forms of eider ducks were found to possess elaborate retia comparable to those in other ducks. In species lacking therete tibiotarsale, the single artery and its counter‐current veins are forming avenae comitantessystem. The number of counter‐current veins increases with foot size and in ravens and crows up to 8 veins were surrounding the artery, resembling the pattern described in the fins of whales. In species of gulls and guillemots, the contact surface between the veins and the artery appeared to be higher in arctic forms than in more southerly distributed birds. The findings are discussed in relation to heat economy, foot size, and ecology of the species. Further, theories for the evolution of the different types of heat exchange systems are presented. It is concluded that no single selective factor can explain the evolution and occurrence of therete t

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1981.tb00617.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractIn this, the first fine structural study of sea cucumber embryology, eggs and embryos ofStichopus tremulusdeveloping at 7.5°C are described from spawning through hatched blastulae. Spawned eggs are at about first meiotic metaphase and are surrounded by a jelly layer that remains around the embryos until hatching. No vitelline coat can be demonstrated, but whether it is truly absent or removed by electron microscopic processing is not known. Insemination initiates a rapid cortical reaction, completed within 2 min., which involves a wave of cortical granule exocytosis and fertilization envelope formation. The compactly fibrous fertilization envelope is about 50 nm thick and appears to consist entirely of ejected cortical granule material (if one assumes that there is no vitelline coat). As the fertilization envelope elevates, no hyaline layer appears in the perivitelline space. The first and second polar bodies are emitted, respectively, at about 9 and 15 min. after insemination. The first seven or so cleavages are equal, radial, and occur approximately every 4 hr. The blastocoel opens up at the four‐cell stage and, during the earlier cleavages, remains connected with the perivitelline space via numerous gaps between the roughly spherical blastomeres. At the 64‐cell stage, these gaps begin to close as the blastomeres start to become cuboidal; in addition, an embryonic cuticle is produced on the apical surface of each blastomere. In embryos of several hundred cells, the blastomeres become associated apicolaterally by junctional complexes, each consisting of a zonula adherens and a septate junction. Several hours before hatching, a single cilium is produced at the apical surface of most blastomeres. At hatching (about 50 hr after insemination), the ciliated blastula leaves behind the fertilization envelope and jelly layer. Swimming blastulae soon begin to elongate in the animal‐vegetal axis, and a basal lamina develops on blastomere surfaces facing the blastocoel. The discussion includes a fine structural comparison of egg coats among the five classes of the phylum Echinod

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1981.tb00618.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractSeasonal variation in the Leydig cells and of the bulbourethral and prostate glands was studied in wild rabbits in southern Sweden, and the variation was correlated with an earlier description of the annual male fertility cycle. The full development of the testes and accessory reproductive organs in the spring was preceded by a peak in Leydig cell activity in January—February. After a depression around the summer solstice, the Leydig cell activity gradually increased, but spermatogenesis and the activity of the accessory reproductive organs continued to decline until late autum

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1981.tb00619.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractCysts among the prolactin cells in the pituitary gland of the nine‐spined stickleback,Pungitius pungitiusL., are most common during and shortly after periods of high mortality that mark the end of the reproductive season. Fish are oldest at this time of year. Nevertheless, cysts may occur in breeding as well as spent fish, and their presence does not relate to changes in oocyte development. They can be induced by starving animals in February, but not in September—October. Starved fish always have small prolactin cells and nuclei. It is suggested that cysts form in older fish in response to stress, be this natural or induced. No correlation was noticed between the condition factor of fish caught in the wild, and the incidence of pituitary cy

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1981.tb00620.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractThe ultrastructure of circulating erythrocytes ofRaja clavataandTorpedo marmorata(Elasmobranchs) andRutilus rutilusandGobio gobio(Teleosts) was comparatively described in relation to their function. The existence of intranuclear hemoglobin and the degradation of cytoplasmic organelles are related to hemoglobin storage. Lysosome‐like vesicles and microtubular marginal bands are also common elements of these cells. Thus, the presence of numerous cytoplasmic organelles in circulating erythrocytes suggests a certain immaturity, in relation to those in mammal

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1981.tb00621.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1981.tb00622.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY