THE PELAGIC NEMERTEAN NECTONEMERTES 465 
sexual characters and reach their full development only with the 
sexual maturity of the animal. | 
In the females, as stated above, the tentacles are entirely 
lacking, such individuals having been described by Verrill (’92) 
under a separate genus and species, Hyalonemertes atlantica. 
As shown in figure 1, the tentacles arise as lateral outgrowths 
of the body walls immediately back of the head. The sections 
show, as described by Cravens and Heath (’06) for N. pelagica, 
and as Biirger (’09) also explains, that the tentacles consist 
mainly of strong muscle bundles directly continuous with the 
muscular layers of the body wall. The musculature is covered by 
a well-developed basement layer (fig. 13, bm) similar to, but | 
thicker than, that of the body walls. The epithelial covering 
has been entirely dislodged, as in the case of the body integument. 
The musculature of the tentacles consists of four distinct sets 
of muscles instead of the three in the body walls. These are: 
a) the outer longitudinal muscular layer (fig. 12, 13, lm’), which 
is a direct continuation of the circular musculature of the body 
but which runs throughout the tentacle longitudinally; b) the 
circular muscular layer (cm’), of great thickness, which is derived 
from the longitudinal body muscles, which change their direction, 
first becoming diagonal and then assuming a circular or spiral 
course through the whole extent of the tentacle; c) the inner longi- 
tudinal muscular layer (figs. 12, 13, calm) which arises mainly from 
the circular muscles of the body; the latter become much thicker 
at the base of the tentacle, sending off not only the outer longi- 
tudinal muscles of the tentacle, but also oblique bundles which 
pass through the longitudinal muscles of the body wall to form 
this internal longitudinal layer of the tentacle; d) the dorsoventral 
bundles (dvm) which are here very highly developed and pass at. 
right angles through the inner longitudinal muscles to connect 
the dorsal and ventral portions of the circular tentacular muscles. 
As shown in figure 13, these dorsoventral bundles are continuous 
laterally with the circular muscles, the individual bundles sepa- 
rating from this more and more toward the median line of the 
tentacle. 
