coe: nemerteans of west and northwest coasts. 263 



point where the pylorus opens into the intestine, but increase in 

 number farther back. The mode of development of the ova is most 

 clearly illustrated in the single specimen sectioned. There is but a 

 single ovum developed in each follicle, and it is a simple matter to 

 Hnd these latter in all stages of development from the undifferen- 

 tiated germinal epithelium to the follicles Avith nearly mature ova. 

 The genital glands (PI. 20, fig. 122) are formed in the outer portions 

 of the parenchyma of the body cavity and just beneath the inner 

 zone of longitudinal muscles, as in other nemerteans. 



In the earliest stages that it is possible to distinguish the follicles, 

 they appear as a continuous mass of granular cytoplasm containing 

 several nuclei, but without cell boundaries. One of the nuclei is 

 many times the size of the others, and contains a considerable num- 

 ber of large nucleoli. The whole cytoplasmic mass is surrounded 

 with a delicate membrane, on the inner side of which, and buried 

 in the cytoplasm, are a number of flattened nuclei. The mass of 

 cytoplasm later assumes a conical form, with the apex directed into 

 the muscles of the body walls (PI. 20, fig. 125). 



The single large nucleus mentioned is to form the germinal vesicle 

 of the ovum, and is almost always situated in the portion of the 

 cytoplasm farthest from the apex. The small differentiated nuclei, 

 which belong to the nourishing cells of the follicle, are most abun- 

 dant near the apex (PI. 20, fig. 125). 



On the side of the germinal vesicle nearest the base of the cyto- 

 plasmic mass, a conspicuous and deeply staining yolk-nucleus is 

 present in all except the earliest and latest stages. It is most 

 highly developed, however, when the ova are about half grown, 

 and lies as a broad cap directl}^ against the nuclear membrane. 

 The nucleoli of the germinal vesicle are most abundant in the vicin- 

 ity of the yolk nucleus (PI. 20, fig. 126). 



As the cytoplasmic mass increases in size, the greater portion of 

 the cytoplasm surrounding the germinal vesicle gradually becomes 

 separated into a large central mass, which is to form the egg cell, 

 and a thin superficial layer in which a number of small undiffer- 

 entiated nuclei are situated, and which forms the follicle (PI. 20, fig. 

 126). A delicate cell membrane now forms about the greater por- 

 tion of the egg cell, but the cytoplasm of this cell still remains 

 directly connected wdth the superficial cytoplasm of the follicle at a 

 number of points. The broadest of these connections lies at the 



