INTRA-OVARIAN EGG OF SOME OSSEOUS PISHES. 71 



The smallest ova I saw were those of Gadus seglefinus, 

 which measured only 00- 11 mm. in diameter (fig. 1). By far 

 the greater portion of the egg was taken up by the nucleus, 

 and many of the numerous nucleoli were already ranged 

 round the inner surface of the nuclear membrane. A small 

 zone of protoplasm covered the nucleus outside. Apparently 

 there was no cell-membrane. The follicular layer was like- 

 wise absent. 



In the next larger size, such as we find in fig. 2, which was 

 taken from the gurnard's ovary, we find that the protoplasm 

 surrounding this nucleus is divided into a dark and light 

 zone. The explanation of this peculiar feature was given in 

 Chapter II. Among the nucleoli some are frequently of a very 

 large size. In figures 6 and 7 we now notice a follicular layer 

 surrounding the yolk and bulging somewhat into it, but the 

 cells composing it are large and not numerous. In fact at first 

 a few cells cover the whole of the ovum. 



I have not arrived at any definite conclusion as to the origin 

 of the follicular layer. There are three possible ways in which 

 it might have arisen : 



1. From outside the egg, by an aggregation of epithelial 

 cells round the ovum, as in Elasmobranchs (Balfour). 



2. From outside the egg by connective tissue or endothelial 

 cells collecting at the periphery of the ovum. Teleosteans 

 (His, Ovsiannikov) . Cephalopoda (Lankester). 



3. From inside the egg : 



a. From the vitellus as in Ascidians (Sabatier). 



b. From the nucleus as in Ascidians (Roule, Fol). 



Myriapods (Balbiani). Orthoptera (Will). 

 Although some of my observations seem to show that the 

 follicular epithelium takes its origin from the interior of the 

 egg, others point the opposite way, and, on the whole, I 

 think it would probably be more correct to assign its origin 

 to the connective tissue. At any rate it is ready formed 

 before an egg-membrane can be discovered. Brock can give 

 no opinion as to the origin of the follicle. According to 

 His the very young ova are often surrounded by a double 



