摘要:

AbstractSince the turn of this century it has been suggested between whiles that brachiopterygians (i.e. the species ofPolypterusandCalamoichthys) are actinopterygians. One of the arguments used recently by advocates of this widespread contention is the dermohyal, an exoskeletal branchial‐arch element which they assert occurs in both groups. However, this argument has to be rejected: the dermohyal does not exist in brachiopterygian fishes. The writer proposes to maintain the view that brachiopterygians are not actinopterygians until better arguments to the contrary are forthcomin

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1986.tb00843.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractComplete removal of a fat body in female toads did not affect the oocyte populations of the ipsilateral ovary with intact blood circulation. It is argued that the inverse relationship in development typical of amphibian fat bodies and gonads does not reflect direct functional relations between the two organs, but may express shifts in anabolic patterns with the onset of sexual maturation.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1986.tb00844.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe fine structure of the female gonad ofVarroa jacobsoniis described. There are two components: the ovary proper and the so‐called lyrate organ. The ovary is the place where oocytes mature, embedded in a supporting tissue composed of two cell types: somacells 1 and somacells 2. The lyrate organ has a nutrimentary function and is comprised of two components: supporting cells and nutritive tissue. The supporting cells are similar to the somacells 2 in that they contain abundant microtubules. The nutritive tissue is an extensive syncytium. It is connected with the oocytes via intercellular bridges, the nutritive cords. Oocytes and nutritive tissue are thought to have derived from common stem cells. From fine structural evidence it is concluded that ribosomes are one of the most important components to be transported via the nutritive cords into the oocytes. However, an increase in number of mitochondria in the middle‐stage oocytes may also be a consequence of transport of these organelles from the nutritive tissue into the oocytes. Further characteristics make plausible that the interdependences of oocytes and nutritive tissue are comparable to those found in meroistic ovarioles of insects. The somatic components do not seem to be as important as the follicle cells of insects, however. It is assumed that the evolution of a nutrimentary oogenesis speeds up embryogenesis. Thus, the differentiation of the female gonad ofVarroa jacobsonimay have facilitated the species' adaptation to a development completed in a short and limited time within the shelter of the covered brood cell of the

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1986.tb00845.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractLabeled inhibitor autoradiography showed that carbonic anhydrase (CA) occurs in (1) the epithelium, (2) free odontoblasts and fibroblasts, (3) row odontoblasts and their membranes surrounding the calcareous parts and (4) extracellular areas. Extracellular CA occurs in areas where fibroblasts and collagen fibers are abundant. The localization of CA suggests that CA facilitates the movement of CO2through the membrane and/or extracellular spaces to promote calcification.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1986.tb00846.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe plumula is enclosed by a single layer of epithelial cells. There are two types of odontoblasts: syncytial and free odontoblasts. Syncytial odontoblasts are arranged linearly on the abaxial side and have a highly active Golgi complex, rough endoplasmic reticulum, large and round mitochondria, and small coated vesicles indicative of a high level of secretory activity. Free odontoblasts cluster on the adaxial side and have patchy chromatin and little cytoplasm. The free odontoblasts migrate to the abaxial side, where their structure changes to that of syncytial odontoblasts. Calcareous deposits are formed intracellularly by syncytial odontoblasts within two membranes: an outer plasma membrane and an inner vacuolar membrane. The vacuolar membrane has organic particles on the surface of the membrane. There is no trace of organic matter within the calcareous deposit. Fibroblasts are located on the adaxial side. Collagen fibers are located primarily on the adaxial side adjacent to the calcareous depositing membranes and between free odontoblasts, but they are not located in the deposits. Collagen fibers may play a role in cell migration and thus in calcification. The morphological changes of the plumulae are closely related to calcification.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1986.tb00847.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractLight and transmission electron microscopy have been used to study the gastrodermal gland cells of the tricladDugesia gonocephalas.l. The events involved in the ultrastructural transformation and the secretion process in these cells were followed at four different stages in both fasted and fed animals. During the feeding stage their secretory granules are directly discharged into the intestinal lumen by means of a secretion process of the holocrine type that is described in this paper. It is suggested that such secretions contribute to extracellular digestion and that disintegration of the gland cells is accompanied by a differentiation of neoblasts into new gland cells, reflecting a turnover of gland cells during the triclad digestive stages.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1986.tb00848.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractMorphological evidence indicates that the endolymphatic sac of anuran amphibians is involved in the morphogenesis of most statoconia (aragonite crystals). The cells frequently show the aspect of an intense secretory activity, their cytoplasm being totally occupied by a number of vesicles the contents of which might be expelled into the lumen forming the organic—or at times mineral—components of statoconia. Moreover, evidence is presented that another function of the endolymphatic sac might be involvement in a resorptive mechanism for endolymph and for CaCO3mobilization from aragonite crystals. In fact, these show clear signs of erosion, consistent with a role as a labile calcium deposit played by the calcareous formations of the endolymphatic

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1986.tb00849.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY