4:30 
W. A. HASWELL. 
From the unbroken appearance of the limiting line of the 
surface ou which the vertical lines terminate, I incline to the 
opinion that no such communications exist. 
The details of the arrangement of the vessels differ in the 
different species. The main trunk soon bifurcates to form 
anterior and posterior main vessels, which give off numerous 
branches to ail parts of the body. A large vessel runs along 
the axis of each of the tentacles. 
Given off from the larger vessels in the body is a system of 
fine, thin-walled capillaries, which are most abundant near 
the dorsal surface, where they form an extensive plexus. 
A limited number of ciliary flames are to be detected in 
the living animal distributed throughout various parts of the 
body and the tentacles. The relation of these to the vessels 
of the excretory system still remains undetermined. In no 
case was a nucleus observed in close relation with the ciliary 
flame. 
The walls of the larger vessels consist simply of a fine- 
grained, structureless protoplasmic material. Here and there, 
usually at long intervals, are the nuclei of the elongated cells 
of which the walls are composed. These are comparatively 
few in number even in the larger species. Their presence 
and their relations to the vessels are best observed in longi- 
tudinal sections — most readily in the tentacles, in which snch 
appearances as those represented in figs. 16, 17, 18 of pi. x of 
my “Monograph ” are i*eadily recognisable. 
Some of the excretory vessels end in certain specially 
modified large excretory cells. The branch in question, 
sometimes fairly thick-walled, sometimes very delicate, enters 
the cell and breaks up into a richly ramifying and anasto- 
mosing system of minute capillaries within its substance. 
The first trace of the system of excretory vessels makes its 
appearance at a very early stage in the history of the embryo. 
In a blastoderm in which the endocoele has become developed, 
bnt is still very small, and is bounded by thick massive cells, 
there may be observed (PI. 25, figs, 15 and 16) on each side 
in close apposition two cells which have the appearance in 
