SOME PKOBLK.MS OF REPRODUOTION. 603 



Merogonic fertilisation lias been obtained also by cutting- 

 the egg in pieces and by piercing tlie vitelline membrane so 

 that a portion of the egg cj'toplasm protrudes and is separated 

 off as an " extra-ovate." The remarkable condition of the 

 egg in Alcyonium, where Hickson tells us that the nucleus 

 disappears completely as the egg matui-es, suggests that in 

 this group the germ-nucleus is entirely of spermatic origin 

 as in artificial raerogony. Clearly Ave cannot speak of 

 '^merogony" where the entire egg is present to receive 

 the sperm if we pay any attention to the etymology of this 

 wordj and it is hardly old enough for ns to forget it. But the 

 essence of raerogony is that tbe cytoplasm of the germ is in 

 this case almost wholly of maternal origin (with the above 

 reservation) and the nucleus is wholly male. Therefore an 

 Alcyonian germ before segmentatioUj from which the unim- 

 portant ablation of a portion of the cytoplasm had been made, 

 would be exactly equivalent to the merogonic germ of an 

 Echinoderm. We will refrain from the creation of a new 

 term to cover tliiH process. 



We have been accustomed to regard the presence of double 

 the number of chromosomes in the germ and its offspring 

 down to the new reducing divisions as resulting from the 

 fusion of the two pairing-nuclei. Nay, in some cases at least, 

 the fusion of the nuclei may be hardly complete, and this 

 partial independence may long persist in the developing- cells 

 of the embryo. On the other hand, Delage has recently shown 

 that in all embryos of Echiuoderms, whether from oosperms, 

 from parthenogenetic eggB with one polar body, or from mature 

 oospheres that have formed two polar bodies, as well as from 

 merogonic syugamy, the number of chromosomes is the full 

 (double) number characteristic of the adult and of the un- 

 reduced reproductive cells. Yet in the case of the mature 

 parthenogenetic oosphere, and in the merogonic germ, the 

 start is made with the half number of chromosomes; and the 

 nucleus must therefore have the power of doubling them so 

 as to suit the needs of the germ, wdiich is habitually formed 

 by cytogamy, and so normally possesses the doubled number. 



