42 WESLEY R. COE. 



organs by which the sexes when mature may be held together 

 until insemination occurs. For it may be assumed that fertiliza- 

 tion of the eggs takes place within the body of the female, as in 

 several well-known littoral and terrestrial species. The early 

 formation of the oviducts indicates that this is probable, although 

 we have as yet no direct evidence that it actually occurs. More- 

 over, it may be not unreasonable to suspect the possibility of 

 embryonic development within the mother's body, which in the 

 known viviparous forms is often associated with eggs of unusual 

 size, as in Geonemertes, for example (Coe, '04). 



The position of the sperm ducts on the ventral surface of the 

 head just anterior to the tentacles, where they could be most 

 effectually pressed against the open oviducts of the female, is 

 a further indication that internal fertilization takes place. And 

 finally, the highly muscular walls of the spermaries (Fig. 8), 

 which are found only in bathypelagic species, doubtless serve 

 for the forcible ejection of the spermatozoa through the slender 

 sperm ducts which open at the summit of small extensible 

 papillae. The weakness of the musculature of the body walls 

 is thus compensated for by the special musculature of the 

 spermary. In Bathynectes murrayi Brinkmann finds similar 

 muscular spermaries connected with slender sperm ducts which 

 extend as penes far beyond the surface of the body (Figs. 15, 16, 

 pe), as described below. Such a condition indicates that the 

 sperm ducts may be actually inserted into the open oviducts of 

 the female. Then by the contraction of the musculature of the 

 spermary some of the spermatozoa contained in the latter would 

 be forced into direct contact with the one or two large ova which 

 each ovary contains. The smaller genital papillae of Nectone- 

 mertes may function in a similar manner. 



In littoral and terrestrial species where fertilization takes place 

 within the body of the female the two worms, after coming in 

 contact, secrete a great abundance of mucus which surrounds 

 the two animals as a sheath and prevents the escape of the 

 spermatozoa after they have been discharged by the male. 

 These bathypelagic species, on the other hand, are but poorly 

 supplied with mucus secreting glands and hence appear to require 

 the actual introduction of the spermatozoa into the oviducts in 

 order that fertilization may be assured. 



