The Germ Cell Cycle in Animals

ring cell division, maturation, and fertilization are contained in Chapters I and II. We may recognize a rather definite chromosome cycle as a part of the germ-cell cycle, and it is to certain events in this chromosome cycle that our attention will be directed in the following paragraphs. It is best to begin our discussion, as in the general reviewof the germ-cell cycle (Chapter II), with the par- thenogenetic or fertilized egg after the maturation processes have been completed, and to exclude all references to the accessory chromosome until later. It may be pointed out first that the number of chromosomes in the cells of any individual of a species is, with few exceptions, constant. Thus the thread worm of the horse, Ascaris megalocephala var. univalens, has two; A. megalocephala var. bivalens, four; the nematod, Coronilla, eight; the mole cricket, Gryllotalpa vulgaris, twelve; the bug, Pentatoma, fourteen; the rat, sixteen; the sea urchin, Echinus, eighteen; the ... --This text refers to an alternate Paperback edition.