COE : NEMEKTEAN8 OF WEST AND NOETHWEST COASTS. 67 



and become disintegrated to furnish food materials for tlie single 

 large ovum. Before the maturity of the ovum the oviduct is in 

 free communication with the exterior of the body, and through this 

 duct spermatozoa fi'om another individual gain access to the ovary. 

 Here they may remain alive for some time, one of them fertilizing 

 the ovum at its maturity. The duct to the exterior then closes up 

 and the fertilized ovum begins its development. In the course of 

 several Aveeks the egg gives rise to a slender, whitish worm fully 

 provided with a delicate proboscis armature and with practically all 

 the organs of the adult except the sexual glands. This worm rup- 

 tures the body wall of the adult and gains access to the outer world. 



Spermatogenesis. — The details concerned in the process of forma- 

 tion of the spermatozoa have not yet been made fully cleai" for any 

 species of nemertean. The most complete accounts are those by 

 Lee ('87) and Burger ('95). In s})ermaries which are approaching 

 maturity Hve different elements can be distinguished : (</) the fol- 

 licular cells, {b) spermatogonia, (c) spermatocytes, and {d) sperm- 

 atids which become transformed into {e) ripe spermatozoa. 



The follicular cells form the lining of the gonad and the duct by 

 which the mature spermatozoa are discharged. They are similar to 

 those of the ovaries described above. All the other cells are col- 

 lected into groups in various parts of the gonad, each group contain- 

 ing only one kind of cell. 



The last generation of spermatogonia are distinguished by having 

 large, oval nuclei and comparatively little cytoj^lasm. They divide 

 to form the secondary spermatocytes, which have very sharp nuclei 

 and distinct cell membranes and are naturally considerably smaller 

 than the cells fi-om which they arise. They divide to form the sperm- 

 atids which collect in similar groups and are distinguished by their 

 small size and the eccentric position of the nuclei. Each spermatid 

 is doubtless transformed into a spermatozoon, although the details of 

 the process have not been fully observed. In certain species a single 

 spermary occupies the space between two adjacent intestinal lobes, 

 while in other forms, as in Gononemertes (Bergendal, : 00") and 

 Carcinonemertes (Coe, :02), the number of spermaries maybe 

 greatly increased, so that they may occupy the whole circumference 

 of the body internal to the muscular walls (Text-fig. 28) . 



The mature spermatozoon consists of head, middle-piece and tail, 

 although the differentiation of parts is not always very conspicuous. 



