1NTRA-0VARIAN EGG OP SOME OSSEOUS PISHES. 57 



way, assuming all sorts of shapes. Some are crescent-shaped, 

 some are like rods, and others again are reduced to small 

 specks or angular fragments. Now what is the significance of 

 all this ? 



To commence with the relation of the dark protoplasm 

 towards the light one, I may previously state that this division 

 of the contents of the ovum has been seen by several authors 

 not only in fishes and amphibians, but also in invertebrate 

 forms. Bambeke 1 observed a division of the protoplasm into 

 two zones in the young ova of Leuciscus rutilus, Hippo- 

 campus antiquorum, and Lota vulgaris. Eimer 3 believes 

 in the idendity of His' " Rindenschicht " with His' " Zonoid 

 layer; " his figures, however, show clearly that in young ova, at 

 any rate, it corresponds to the light protoplasm which I described, 

 in distinction to the more granular part internally to it. The 

 fact that the yolk is divided into zones has also been observed in 

 Sepia by Lankester. 3 Finally, my friend Dr. Will* has noticed 

 the same phenomenon in Orthoptera. No doubt the forma- 

 tion of protoplasmic rings round the nucleus of the growing 

 egg has been seen in a still greater number of animal groups 

 than I have just enumerated. 



I think there can be little hesitation in regarding the dark 

 central protoplasm as owing its origin to the nucleus, although 

 there appear to be cases, such as recorded by Lankester/ in 

 which the protoplasm is nourished entirely from without. 



But a difficulty presents itself here. Has the dark part 

 originated by a simple transformation of the light portion, or 

 has another substance been added to the protoplasm from the 

 nucleus causing this change ? The latter seems the most 

 probable of the two cases. This view is considerably strength- 



1 Bambeke, " Recherches sur Pembryologie des poissons osseux," • Mem. 

 cour. Acad. Belg./ vol. xi, 1875. 



2 Eimer, " Untersuchungeu iiber d. Ei d. Reptilien und Eische,' « Arcbiv 

 f. mikr. Anat.,' vol. viii, 1872. 



3 Lankester, E. Ray, " Contributions to the Developmental History of the 

 Mollusca," ' Philosophical Transactions,' 1875. 



4 Will, " Bilduugsgeschichte und morphologischer Wertli. d. Eies von Nepa 

 und Notonecta," ' Zeitschrift f. wiss. Zool.,' vol. xli, 1885. 



