. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. PRESENT PROBLEMS IX EVOLUTION AND HEREDITY. :}G3 iiiquo, and stimulated by Wcisuiaiiii's prediction that spermatozoa would also be Ibuud to extrude i)olar bodies, this author exanuued all stages in the peculiarly favorable germ cells of the thread-worm of the horse {Asc<(ris mcgaJovcphdla). lie made the suri)rising discovery that o^a and spermatcj/.oa are formed in a substantially similar manner by rcjxatcd divisions, the single differen
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. PRESENT PROBLEMS IX EVOLUTION AND HEREDITY. :}G3 iiiquo, and stimulated by Wcisuiaiiii's prediction that spermatozoa would also be Ibuud to extrude i)olar bodies, this author exanuued all stages in the peculiarly favorable germ cells of the thread-worm of the horse {Asc<(ris mcgaJovcphdla). lie made the suri)rising discovery that o^a and spermatcj/.oa are formed in a substantially similar manner by rcjxatcd divisions, the single difference being that the last jiroducts of division among the sperm cells are eftective speinmtozoa, capable of development in fer- tilization, while the last i)rodiicts of division in the ovary are, first. Thk Matcratiox of Ova, or of Polar Bodies in Ascaris. (Knmi Weismnhn afto Hortzwiir.) A. original fjcnn-ccll in embryonic !r''rm-Uiyli;tin'4 oC tirst jiolar body. 0\iiini slill contains 4 rods; F, Second i)olar l)o(ly extruded : Ovimii mat urc w it li 1! ro<ls. the true ova, and, second, the abortive ova. (polar cells), inca])able of development. In both ova and spermatozoa the nucleus coidains but cue-half the chromatin which w ty])ic:il nucleus contains; in the case of A. wefjrdocepJiaht each of the germ cells contains but two chrom;i somes while the normal body cells contain four. The manner in which this maturation of the germ cells for conjugation is brought about is beiuitifully shown in these diagrams, taken from Weismann's essay, "; You observe that the nund)er of chromasomes in the primary germ cells is four (Figs. 11 and 12, A). Then are fornu-d by subdivision the ovum and si)erm "mother cells," in which the chro- matin substance is doubled, so that we observe eight chrounisomes The mother cells then divide and the chronmtin is reduced to tour rods, a second division rai)i(lly Ibllows whereby the chromatin is reduced. Please no
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