Ryder.] l-O [May 16. 



fission in the course of the development of the male cell is such as to give 

 its quiescent nucleus, in its restricted cytoplasmic field, a karyokinetic 

 momentum, so to speak, which will be expressed as segmentation as soon 

 as it is fused with the female pronucleus in a large cytoplasmic field, in 

 the egg, where karyokinesis or nuclear motion again becomes possible. 



In the same way the tendency towards developing a karyokinetic mo- 

 mentum must occur in the egg, owing to the limited number of rapidly 

 successive karyokineses in the expulsion of the physiologically differenti- 

 ated chromatin in the form of the polar bodies, which may themselves 

 manifest subsequent spontaneous segmentation, or even make abortive 

 unions with spermatozoa, which are abortive only, probably, because of 

 the small size of the cytoplasmic field. If the results of Hertwig and 

 Boveri in fertilizing non-nucleated fragments of the cytoplasm of the eggs 

 of Echinoderms are correctly reported, it is certain that the spermatozoon 

 is in a condition of karyokinetic tension, which lacks only a cytoplasmic 

 field in which to find expression as segmentation. 



The views here developed also harmonize with what is known of the 

 behavior of the nuclei of conjugating Infusoria. It is only the micro- 

 nuclei or paranuclei which enter into the reciprocal conjugation. The 

 macronuclei or functional centres of control of the physiological energies 

 of these animals never enter into the process, but are disintegrated and 

 lost in the cytoplasm, while some of the new micronuclei now formed be- 

 come, after conjugation and reciprocal fertilization, the new functional or 

 physiological nucleus, and one or two remain, for the time being, at least, 

 as passive, and probably functionless, micronuclei.* 



It may be supposed by some that the foregoing account is merely a 

 recapitulation of Weismann's hypothesis respecting the significance of the 

 polar bodies. Not so ; Weismann's very elaborate and artificial methods 

 have no charm for me. He is continually trammeled by his own cumber- 

 some hypothesis of a germ-plasma. But he is probably right as far as 

 assuming that the first polar body represents chromatin of a " histoge- 

 netic" character, but I should say in a totally different sense from that 

 which he implies. I should also agree with him that it is expelled in 

 order that the egg may revert to its unspecialized condition, but again in 

 a widely different sense from that which he holds. 



Unfortunately for Weismann, he renders his hypothesis utterly improb- 

 able from the necessity of working out a second hypothesis to account for 

 the expulsion of the second polar body, in order to save his first unfounded 

 assumption respecting the immortality of the germ-plasma. That doc- 

 trine, driven to its logical conclusion, leads ultimately to the molecular 

 disintegration of the vast series of ancestral plasmas, finally present in 

 the egg in the course of a vast series of generations. Accordingly the 

 only way to save his hypothesis was, as soon as certain parthenogenetic 



*In this I follow the recent researches of Maupas : " La Rajeunissement Karyogam- 

 ique chez les Cilies." Arch. Zool. Exper. et Generale. 2e Ser., Tome vii, Nos. 1 and 2, 

 1839. Pp. 149-320 el seq. 



