Nos. IAND2.] COTYLASPIS INSIGNIS. 35 



same appearance. The follicles are bounded by an extremely deli- 

 cate structureless wall, enclosing a number of yolk cells in various 

 stages of growth. The smallest and earliest cells (Fig. 58) have a 

 diameter of .01 mm. and bear considerable resemblance to the 

 youngest ova, having a large nucleus with a large nucleolus, scat- 

 tered grains of chromatine and a small amount of cytoplasm. 

 Besides these there are larger cells in which the cytoplasm is more 

 abundant and is beginning to be pervaded .with minute droplets of 

 yolk. There are also in the follicles still larger cells, of a diameter 

 of .02 mm. (Fig. 61), where a cell wall is seen and next it a layer 

 of yolk droplets, then a hollow space, and then a central mass of 

 protoplasm with a nucleus. This is the final form of the yolk cell, 

 in which it passes down to and is found in the yolk receptacle. 



The yolk receptacle lies between the ovary and the spermary. It 

 is a triangular cavity, two angles are at the junction of the two 

 ducts from the vitellaria, the third angle being at the origin of the 

 passage leading out to the oviduct. The wall of this organ can be 

 traced in living specimens under compression out into the three 

 different ducts and by pressure the contents can be forced out 

 through the ducts. The wall in sections is seen to be distinctly 

 cellular as indicated by the presence of flattened nuclei, unlike that 

 of the vitellarian follicles in which nuclei can not be recognized. I 

 have not observed any muscular tissue in this wall in specimens in 

 which it is easily seen in the oviduct. The yolk receptacle is 

 filled with yolk-cells identical in appearance .with the largest cells 

 in the vitellaria, which clearly have merely been collecting and 

 waiting here till an egg cell shall descend, when they will join it, 

 and in the oviduct near by acquire a shell, thereby completing the 

 egg. In many of the trematodes there are two organs at or just 

 beyond the junction of the yolk-duct and the oviduct, the ootype 

 in which the embryo is formed and the shell gland, a gathering of 

 cells surrounding the ootype which produces the substance of 

 which the shell is composed. I have not succeeded in recognizing 

 either of these as distinct organs in Cotylaspis; doubtless here the 

 ootype is never more than a slightly specialized part of the oviduct. 

 Thus in Macraspis Jagerskiold '99 refers to it by name, though 

 in his figure no distinct part is represented to correspond. Accord- 

 ing to Stafford a distinct enlargement of the oviduct is found just 



