586 THE STRUCTURE AND DEVELOPMENT 



in the embryo. In many instances they form polynuclear 

 masses, not divided into separate cells, generally, however, the 

 individual ova are distinct. The ova in these nests are on the 

 average rather smaller than during the embryonic periods. The 

 nests are frequently quite superficial and at times continuous 

 with the pseudo-epithelium, and individual ova also occasionally 

 occupy a position in the superficial epithelium. Some of the 

 appearances presented by separate ova are not unlike the figures 

 of Ludwig, but a growth such as' he describes has, according to 

 my observations, no existence. The columns which he believes 

 to have grown into the stroma are merely trabeculae connecting 

 the deeper and more superficial parts of the germinal epithelium ; 

 and his whole view about the formation of the follicular epithe- 

 lium round separate ova certainly does not apply, except in rare 

 cases, to Scyllium. It is, indeed, very easy to see that most 

 freshly formed ova are derived from nests, as in the embryo ; 

 and the formation of a follicular epithelium round these ova 

 takes place as they become separated from the nests. A few 

 solitary ova, which have never formed part of a nest, seem to be 

 formed in this stage as in the embryo ; but they do not grow 

 into the stroma surrounded by the cells of the pseudo-epithelium, 

 and only as they reach a not inconsiderable size is a definite 

 follicular epithelium formed around them. The follicular epi- 

 thelium, though not always formed from the pseudo-epithelium, 

 is of course always composed of cells derived from the germinal 

 epithelium. 



In all the ova formed at this stage the nucleus would seem 

 to pass through the same metamorphosis as in the embryo. 



In the later stages, and even in the full-grown female of 

 Scyllium, fresh ova seemed to be formed and nests also to be 

 present. In Raja I have not found freshly formed ova or nests 

 in the adult, and have had no opportunity of studying the young 

 forms. 



Summary of observations on the development of the ovary in 

 Scyllium and Raja. 



(i) The ovary in the embryo is a ridge, triangular in sec- 

 tion, attached along the base. It is formed of a core of stroma 

 and a covering of epithelium. A special thickening of the epi- 



