. Senescence and rejuvenescence. Age; Reproduction. THE GAMETES IN PLANTS AND ANIMALS 337 differentiation of the motor mechanism from a cell of the usual sort. But in some cases, as in the angiosperms among plants (Figs. 152, 153), in Ascaris (Fig. 165), and in the Crustacea (Figs. 168-70) among animals, the male gamete is almost or quite non- motile. Even in such cases, however, it is none the less a highly specialized cell. In the angiosperms among plants a morphologically differentiated cyto- plasmic mechanism is absent, but the history, form, and behavior of the nucleus attest its speciaHz
. Senescence and rejuvenescence. Age; Reproduction. THE GAMETES IN PLANTS AND ANIMALS 337 differentiation of the motor mechanism from a cell of the usual sort. But in some cases, as in the angiosperms among plants (Figs. 152, 153), in Ascaris (Fig. 165), and in the Crustacea (Figs. 168-70) among animals, the male gamete is almost or quite non- motile. Even in such cases, however, it is none the less a highly specialized cell. In the angiosperms among plants a morphologically differentiated cyto- plasmic mechanism is absent, but the history, form, and behavior of the nucleus attest its speciaHzation. In Ascaris (Fig. 165) the pecuHar structure of the cell shows that it has departed far from the generaHzed form of the embryonic cell. In the crustacean sper- matozoa (Koltzoff, '06a) the skeletal or supporting structures are extensively developed, but according to Koltzofi {'06b, '08), such structures are present in other spermatozoa also. Ballowitz' ('86-'o8) extensive studies of the finer structure of the spermatozoa also demonstrate the morphological com- plexity of these remarkable cells. In the more highly differentiated forms there remains no trace of the ordinary amorphous cytoplasm of the cells from which they arise: all has either under- gone breakdown as a source of energy or has been transformed into the fibrillar or other structures of the spermatozoon. The development of the female gamete follows a very different course, but is none the less a process of spe- ciaHzation and morphological differen- tiation. Figs. 123, 125, 126, and 128. Figs. 158-161.—Develop- ment of spermatozoon from spermatid in the guinea-pig: Fig. 158, beginning of trans- formation; Fig. 159, beginning of development of tail; Fig. i6o, side view after formation of the thin flat head; Fig. i6i, mature spermatozoon. From Meves, ' Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of t
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectreproduction, bookyea
