tailieunhanh - Reproductive System Structure, Development and Function in Cephalopods with a New General Scale for Maturity Stages

Since the early 1980s, much time and effort has been expended in trying to understand the relative contributions of different social factors in mortality decline (especially declines in infant and child mortality) and in reductions in fertility. In these debates, the schooling level (number of years attended) of a young mother has often been portrayed as the single most powerful correlate of reductions in the infant and child mortality of her children, and (to a lesser but still very considerable degree) to reduction in her completed family size. These correlations have been observed in almost every country and region at. | http J. Northw. Atl. Fish. Sci. Vol. 12 63-74 Reproductive System structure Development and Function in Cephalopods with a New General Scale for Maturity Stages A. I. Arkhipkin Atlantic Research Institute of Marine Fisheries and Oceanography AtlantNIRO 5 Dmitry Donskoy street Kaliningrad 236000 USSR Abstract The main types of reproductive system structure development and functions in cephalopods are described from personal observations and use of the literature. There is one type in malesand three in females which are order specific. These have provided a basis for examining possible evolutionary trends in reproductive system development and in reproductive strategies within coleoid cephalopods and for developing a general scale for maturity staging for males and females. Development of the cephalopod reproductive system consists of two main phases. The first includes sexual cell differentiation growth and maturation . juvenile phaseand physiological maturation . The second begins after maturation of sexual cells. It includes their transportand accumulation in different parts of the reproductive system and their conversion into spermato-phores in males and eggs with protective coverings in females . physiological maturity functional maturation and maturity . It was found that species with different life styles within each order have similar reproductive systems. This may be attributable to the relative youth in an evolutionary sense of the main groups of living cephalopods. A general scale of seven maturity stages for cephalopods was developed. Distinct characteristics of each stage are described and supplemented with a generalized drawing of gonad structure. In the first phase of reproductive system development maturity stages are distinguished by the degree of development of the gonad and accessory glands. In the second phase maturity stages are distinguished by the fate of the mature sexual cells particularly by their transport and .

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