THE PELAGIC NEMERTEAN NECTONEMERTES 471 
back it extends, being about one-third the diameter of the ventral 
core in the middle of the body and only one-tenth of this diameter 
near the posterior end of the body. 
These worms, in common with many pelagic nemerteans, lack 
both cerebral and frontal sense organs. 
REPRODUCTIVE ORGANS 
The sexual dimorphism of the species of the genus Nectone- 
mertes is described above (page 459), and is more fully discussed 
in a recent paper by Coe (20). 
Spermaries 
The spermaries, as in most other truly pelagic nemerteans, are 
limited to the head, there being fifteen or more in an irregular 
elongated group situated ventrolaterally on each side of the 
head (fig. 1). These were correctly described by Verrill (’92), 
but their true nature was not recognized by him. He suggested 
with some hesitation that they might possibly be special sense 
organs. In each of these groups the spermaries appear to be 
roughly arranged in two longitudinal rows, of which one lis dis- 
tally and the other medially to the lateral nerve cord (fig. 1), 
but there is great irregularity in this respect, due to the crowd- 
ing of the spermaries and the irregularities of the contraction of 
the body. Sometimes a partial third row of three or four sperm- 
aries lies internal to the posterior end of the other two, as shown 
on the right-hand side of figure 1. The opening of each gonad 
is situated on the summit of a small papilla, which in some cases 
rises well above the surface of the body wall. An extreme 
development of these papillae has been described by Brinkmann 
(12) for Bathynectes murrayi, where the efferent ducts from 
the spermaries extend from the body as long, slender penes. 
In transverse section of the head of a fully matured individual 
(fig. 6) the spermaries fill the major portion of the space within 
the body walls, crowding the diverticula of the intestinal caeca 
(icd) close up against the dorsal wall of the body and almost 
obliterating its lumen. ‘The lateral nerve cord (In) and the blood- 
JOURNAL OF MORPHOLOGY, VOL. 34, NO. 3 
