460 WESLEY R. COE AND STANLEY C. BALL 
states that he has been able to prove from a large series of speci- 
mens that sexual dimorphism actually occurs and that the lateral 
tentacles develop in Nectonemertes only after the animal reaches 
sexual maturity. Somewhat more recently, Brinkmann (16) has 
found in a closely related species, N. minima Brink, a parallel 
case in which the three males which he had for study showed the 
tentacles in various degrees of development, while the single 
female specimen available for study showed no traces of such 
appendages. He looks upon these peculiar appendages as having 
become specialized to serve as grasping organs by which the male 
is able to cling to the female during the act of insemination. 
There seems little doubt that this interpretation is correct. 
Living as the worms do in the vast areas of the deep sea and not 
limited, as are so many other forms, to a very restricted range of 
depth either at the surface or on the ocean’s floor, these nemer- 
teans doubtless ordinarily live as widely separated individu- 
als. This is evidenced by the rarity with which they are taken, 
even when many hauls of the net are made in the same locality. 
With this separation of the individuals the ordinary methods 
of fertilization which obtain in littoral nemerteans, namely, the 
free discharge of eggs and sperm into the water at the place 
where the two sexes are living, would be extremely hazardous. 
To insure fertilization in this way there is required proximity of 
the sexes in restricted areas. Hence the advantage of making 
insemination reasonably certain by free motility of the animals 
and the provision for their remaining in contact for a period suf- 
ficiently extended to allow for the transfer of the sperm. Both 
these advantages, or necessities, are adequately provided for by 
the muscular tentacular appendages of the male in Nectonemertes. 
Correlated with these adaptations is a peculiar modification of 
the spermaries, which are provided with strong muscular walls, 
as described below, for the forcible ejection of the sperm. Cor- 
related also is the great reduction in the number of eggs produced 
by the female, Here, as in other bathypelagic species, not only 
is the number of ovaries greatly reduced, as compared with other 
nemerteans, but each ovary brings to maturity only one or two 
ova. All the rest of the numerous primitive ova become reduced 
