. The biology of death; being a series of lectures delivered at the Lowell Institute in Boston in December 1920. Death (Biology). 38 BIOLOGY OF DEATH the former are borne in the female, and the latter in the male body. Both sorts undergo a complicated prepara- tion for union, the result of which is that when union does occur each party to it contributes either an exactly equal or an approximately equal amount of hereditary mate- OermCeUa. WSMMi<^0ml^^KSB^0mWM Fia. 9.—Section across the posterior part of an embryo dog-fish (acanthias) of mm., to show the compact cluster of germ cells on
. The biology of death; being a series of lectures delivered at the Lowell Institute in Boston in December 1920. Death (Biology). 38 BIOLOGY OF DEATH the former are borne in the female, and the latter in the male body. Both sorts undergo a complicated prepara- tion for union, the result of which is that when union does occur each party to it contributes either an exactly equal or an approximately equal amount of hereditary mate- OermCeUa. WSMMi<^0ml^^KSB^0mWM Fia. 9.—Section across the posterior part of an embryo dog-fish (acanthias) of mm., to show the compact cluster of germ cells on one side. The germ cells in later stages migrate from this primative position, moving singly or in small groups. Ect, ectoderm: Md, medullary canal or primitive spinal cord; Nch, notochord; Mes, mesoderm: Eni, entoderm: X, cellular strand connecting the germ cell cluster with the yolk. (From Minot after Woods, with the permission of the publishers, G. P. Putnam's Sons). rial. After union has taken place the fertilized ovum or zygote presently begins to divide, first into two cells, these again to four and so on, until by a continuation of this process of division with concomitant differentiation the whole body is formed. As the animal develops by- repeated cell division and differentiation, it is frequently found that at the very early stage the cells which are to be the germ cells of the next generation are clearly re-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Pearl, Raymond, 1879-1940. Philadelphia, London, J. B. Lippincott Company
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