718 PROFESSOR W. C. MSINTOSH AND MR E. E. PRINCE ON 
nuclei, originating as independent segregations of active protoplasm, like the nuclei which 
arise endogenously in the Molluscan ovum, as Professor Ray LANKESTER was the first to 
recognise. In Crustacean ova such nuclei have long been known, though in Onzseus 
it is noteworthy that Bosrerzsky affirms their blastodermic origin and subsequent 
migration ; but this view is not generally accepted. WEISSMAN, too, imagined that in 
the ova of Dipterous insects such structures arise de novo, and without genetic relation 
to nuclei already existing ; but later researches lend little countenance to this opinion, 
and WerssMAN has abandoned his contention. KowaLewsky has described in the yolk- 
matrix of the Annelidan ovum scattered nuclei, endogenously formed and afterwards 
collecting superficially, especially beneath the blastoderm ; they are at first few in num- 
ber, but show rapid increase, and are especially abundant about the time of exclusion. 
He regards the nuclei of the “intermediary layer” in the Teleosteans as originating from 
those of the entoblastice (yolk-) cells. The appearance of free nuclei in the region outside 
the embryonic area in the chick, as described by RauBer (No. 133, p. 570), is a further 
instance of such extra-embryonic nuclear bodies, and the nuclei in the Teleostean 
periblast may have a like origin.* The fact that they differ in shape from the 
spherical nuclei of the dise—being generally more or less elliptical, and often of 
larger size (PI. II. fig. 6, )—points to a non-blastodermic origin. Kuprrer speaks of 
their differentiation, and of delicate contours which appear round them resembling hexa- 
gonal figures, in Clupea (No. 87, p. 205). Lrresounzer observes that they are large and 
granular in Hsow, and along with the matrix in which they lie, they “come from an- 
other source” than the protoplasm and nuclei of the disc (No. 93, p. 494). Ba Four, again, 
comes to the conclusion, while leaving their origin an open question, that there is no 
evidence of their derivation from pre-existing nuclei in the blastoderm (No. 10, p. 109). 
In the living Teleostean ovum it is difficult to watch the actual formation of these 
nuclei ; but Kuprrer describes with some detail the appearance in Clupea of clear spots 
of protoplasm which grow from a speck-like particle to a body 5-6 m in diameter (op. 
cit., p. 201), and E. van Brnepent is no less decided in affirming that these nuclei 
arise ‘‘par voie endogene” simultaneously in the periblast. We have noted that in 
the egg of the cod, towards the end of the first day, the periblast shows only minute 
granules scattered through its translucent protoplasm. The nuclei{ are few at first, 
and close to the edge of the disc, as if some of them had escaped by “hernia.” At other 
parts of the periblast clear vesicles and minute granules occur. Observations do not 
strongly support the view that the nuclei of the periblast migrate from the archiblast, 
but probably they arise in the periblast itself, and it may be that the activity in the dise 
proper stimulates similar activity in the periblast, just as a limited area of irritation in 
* Ryper regards the “ nuclear zone” as homologous with this germinal wall in the chick, and it is certainly note- 
worthy that the nuclei in the latter (the “ white yolk nuclei”) are most abundant below the thickened periphery of the 
blastoderm, and become the nuclei of cells which enter the germ. + Belg. Acad. Sc., No. 6, June 1876, p. 1202. 
~ Kiyastery and Conn (op. cit., p. 199) observed in the cunner the formation of cells round these nuclei on the 
surface of the yolk; but it seems, aceording to Mr G. Brook, that Mr Kinastry has since altered this view (Trans, Roy. 
Soc. Edin., 1887, p. 224). 
