ISBN: 9781130778281

RareBooksClub. Paperback. New. This item is printed on demand. Paperback. 242 pages. Dimensions: 9.7in. x 7.4in. x 0.5in.This historic book may have numerous typos and missing text. Pur… More...

RareBooksClub. Paperback. New. This item is printed on demand. Paperback. 242 pages. Dimensions: 9.7in. x 7.4in. x 0.5in.This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1904 Excerpt: . . . such substance is used by the sperm cells only in limited amountThe first formation of the yolk substance is an elaboration by the vitellocytes (nurse or follicle cells), which are germ cells that have lost their reproductive ability and become nutritive. These have their representatives in the testes in the cells of Sertoli, also nutritive. But the ovarian vitellocytes play a greater part in the growth of the embryo, and accordingly they are larger or more numerous. Further they are segregated to form particular chambers of the ovary, so that the nutritive and reproductive cells occupy different places within the ovary. This is the case in the Rotatoria and some Crustacea (Branchiopoda), and in the Insects, where the egg-tubes that compose each ovary have each a terminal chamber of vitellocytes (Hemiptera), or vitellocyte chambers alternating with egg-cell chambers (Coleoptera). These are all specializations in the arrangement of the nurse cells which mark the ovary as being a more complex structure than the testis. Then there is found in the female of many Insects an apparatus for oviposition, known as the sting or ovipositor, olten of high degree of complication, involving parts of two (or more) segments; this is entirely absent in the male. The female usually guards and protects the young, sometimes with the development of a brood chamber (some Crustacea); that is only exceptionally the case with the male, and sometimes, as in the hemipteron Zaitha, he is forced by the female to carry the eggs against his will. But the males of the Pycnogonida carry the young. From this rapid survey of some of the facts of sexual dimorphism, we find the supposed excellence of the male to consist in what are mainly unimportant morphological characters, of which the (not. . . This item ships from La Vergne,TN., RareBooksClub<