W. Ji. Coe — Anatomy of Cerehratulus lacteus. 505 



single individual discharged at once, a specimen often showing a 

 portion of its genital sacs to be empty, while other sacs are filled 

 with mature ova or spermatozoa. By the first of May, in the vicinity 

 of New Haven, nearly all the genital products have been discharged. 



The genital products are developed in flattened pouches, or sacs 

 (Plate XIV, figs. 10, 11, gs), which alternate with the intestinal 

 caeca. These sacs are closely bordered in front and behind by the 

 double band of dorso-ventral muscles {dm) which lies between each 

 pair of intestinal caeca In the summer, before the genital products 

 begin to develop, the sacs occupy only a narrow \^ -shaped space 

 (fig. 10) just inside the body-muscles. One end of this space lies 

 near the proboscis-sheath above, and the other near the lateral blood- 

 vessel beneath the intestine. It is in this space that the genital 

 products originate. As they mature, the sacs greatly enlarge and 

 finally occupy (figs. 9, 11) fully one-half of all the space within the 

 body-wall. They extend from near the body-muscles (Im) on three 

 sides nearly to the proboscis-sheath and central canal of the intestine 

 {i). In a horizontal section of the body, the sacs are seen to be some- 

 what thicker next the central intestinal canal than distally. They 

 are also thicker above and below than in the middle. When the 

 genital products are nearly mature each sac is pointed into the mus- 

 cular layers of the body-wall at a point between the lateral cord and 

 the median nerve, though somewhat nearer the latter. This pointed 

 extremity forces its w^ay through the muscular layers and the integu- 

 ment, making a duct through which the genital products may be dis- 

 charged. This duct is lined with flattened epithelium. 



The genital sacs are also lined with a flattened epithelium, certain 

 cells of which are destined later to develop into ova or spermatozoa, 

 while others apparently remain unchanged to form the follicles. 

 These epithelial cells have small, elongated nuclei. The cell-walls 

 could not be made out. In the female, when the ova begin to 

 develop, the nucleus of the epithelial cell greatly enlarges and the 

 cell acquires a more definite wall. The young ovum (Plate XIV, 

 fig. 5, ov') has a delicate investing membrane, or follicle (/b), and is 

 imbedded on one side in the loose connective tissue forming the 

 frame-work of the sac. As the ovum increases in size its nucleus 

 develops into the large germinal vesicle which has many germinal 

 spots, of which one or two are much larger than the others. 



The fully ripe, living ovum (fig. 4) is .09'"'" to .11'"'" in diameter 

 and is surrounded by a gelatinous zona pellucida which swells up in 

 contact with water to about twice the diameter of the ovum. The 



