Nos. IAXD2.] COTYLASPIS INSIGXIS. 37 



In Aspidogastcr they are stated by \'oeltzko\v to measure .127 

 mm. by .061 mm. ; this is less than half as large as the correspond- 

 ing dimensions in Cotylaspis. 



They aie of a lemon-yellow color, and are curved as in Fig. 63, 

 which slight bend in the long axis is a very constant character- 

 istic. Near one end is located an operculum, and by irrigating a 

 slide containing embryos with acetic acid I could observe the 

 bursting off of the operculum and the issuing out of the yolk 

 cells, owing to the pressure within. In some cases I found 

 an operculum at each end. The embryo, as usual, consists 

 of a single approximately centrally located embryo-cell, and 

 a surrounding mass of numerous yolk-cells. The spherical 

 embr}-o-cell measures .04 mm. in diameter, and up to the time 

 it is passed out from the parent shows no outward indications 

 of segmentation. In living eggs it is clear and structureless; the 

 nucleus cannot be seen, but in sections this cell, which can be 

 identified by its central position, size and structure, has a distinct 

 nucleus, and in some cases two or even four nuclei were seen. 

 But in no case were two such embryo-cells visible in the em- 

 bryo, which must be a conclusive proof that the segmentation does 

 not take place in the body of the parent. In this Cotylaspis is 

 quite unlike the rest of the kno.wn Aspidobothridse. 



The yolk-cells have distinct boundaries rendered nearly invisible 

 by crowding (see Fig. 63). They are numerous and considerably 

 smaller than the embryo cell (.025 mm. in diameter). They look 

 quite unlike the yolk-cells of the yolk receptacle having a clear 

 peripheral zone and a denser central zone, in the center of which 

 is the nucleus (Fig. 63). This contrasts strongly with the cell 

 before it has become incorporated with the embryo, in which 

 distinct grains of yolk are seen and located at the periphery of the 

 cell, and may be an indication of the beginning of changes related 

 to the nutrition of the egg-cell. 



An attempt was made to follow the development of the embryo, 

 but only a very little has been gotten as yet. As already stated, the 

 egg does not develop in the parent. By keeping recently dis- 

 charged embryos under observ-ation from day to day I found that 

 the egg-cell begins to segment, and that its development progresses 

 as shown in Figs. 66-74. These indicate a total segmentation at 



