BY JAS. P. HILL. 
21 
anterior to the internal openings of the collar canals, two distinct 
spaces exist. 
With regard to the division of the collar coelom into two halves, 
considerable variation exists in this species. Dorsal and ventral 
septa may be entirely absent, the two side halves of the coelom 
then standing, as in Balanoglosms kitpfferi according to Spengel, 
in open communication. 
The dorsal septum when present differs from the normal 
condition in Pi. minuta with regard to its relation to the "roots." 
In that species, according to Spengel, the dorsal septum only exists 
in the posterior part of the collar; two "roots" are situated 
anterior to it, and its anterior free edge always appears to corre- 
spond to one of the "roots." In this species the septum may arise 
in the anterior region of the collar and in front of the most 
anterior root as a fold projecting from the dorsal surface of the 
collar cord and with a free anterior edge, and which reaches the 
outer wall where the first "root" fuses with the collar epidermis. 
The septum then passes between the remaining "roots" to the 
posterior end of the collar. Over part of its course it may be 
interrupted: the ventral connection with the dorsal surface of the 
cord is lost, the septum at the point of interruption appearing as 
a free fold projecting from the inner surface of the outer collar 
wall. Further, in other individuals the front edge of the septum 
may coincide with either the first or the second "root." 
As to the ventral septum (fig. 19, vcs.) when present, it exists 
only in the most posterior part of the collar and there only for a 
very short distance. It may be present when the dorsal is absent. 
In fig. 18 a section passing just anterior to the ventral septum is 
represented. The vessel fold (sh.) arising from the subepidermic 
collar capillaries exists only for a short distance in the posterior 
region of the collar, and is not always so distinct as in the series 
from which this section is taken; posteriorly it unites with one of 
the longitudinal vessel folds to give rise to the ventral septum 
(fig. 19, vcs.). The collar canals and the collar- trunk septum are 
related in this species exactly as in PL minuta. 
