THE PELAGIC NEMERTEAN NECTONEMERTES 473 
secondary spermatocytes (spc’) are naturally much smaller. The 
spermatozoa in their earlier stages are clustered together with 
their heads imbedded in large nurse cells. In the more mature 
spermatozoa (spz), which occupy the lumen of the gonad, the 
slender heads of a hundred or more may lie side by side with 
their tails forming a compact wavy bundle. 
The developmental stages of the peculiar structures described 
above for the fully mature gonad are well shown in some of the 
immature spermaries and are illustrated in figures 15 and i6. 
In figure 15 the seminal vesicle (sv) is seen to consist of a pointed 
outgrowth from the gonad which penetrates the body wall only 
as far as the basement layer. The single layer of cuboidal epi- 
thelium which makes up the wall of the seminal vesicle here 
extends into the body of the gonad for a short distance and then 
terminates abruptly in the muscular layer (m). Spermatogonia 
(spg) lie next the muscular wall, while the body of the gonad is 
filled with spermatocytes (spc). Figure 16 is a tangential section 
of the gonad, showing the muscles and their slender nuclei cut 
lengthwise and the seminal vesicle cut transversely. 
The peculiar modifications of the spermaries and their ducts 
indicate a provision for the conservation of the genital products 
and an assurance of insemination. The significance of the semi- 
nal vesicles, found in no other genus of nemerteans, so far as known, 
is obviously to supplement the spermaries in storing the ripe 
spermatozoa and probably also to aid in their expulsion. The 
powerful musculature indicates a forcible ejection of the sperma- 
tozoa during the act of pairing. And, finally, it is perhaps reason- 
able to conceive of the genital papillae as being capable of eleva- 
tion, with the aid of. the seminal vesicles, far above the surface 
of the body walls, so that they may be placed directly against 
or even into the oviducts of the female. The contraction of the 
musculature of the gonad might then, conceivably, force the 
spermatozoa into direct contact with the egg or pair of eggs in 
the ovary. The two worms are meanwhile held in close contact 
by the muscular tentacles of the male. 
Brinkmann’s discovery (12) that in Bathynectes the sperm 
ducts open on the tips of long, slender processes, which he calls 
penes, supports this hypothesis. 
