6 
Huxley on Lacinularia socialis. 
vessel, closed at the extremity, runs through most of its length, 
which maintains a wavy motion" — p. 98.* 
The following is what I have seen in Lacinularia : — There 
is no contractile sac opening into the cloaca as in other genera, 
but two very delicate vessels, about l-4000th of an inch in dia- 
meter, clear and colourless (fig. 3 m), arise by a common origin 
upon the dorsal side of the intestine. Whether they open into 
this, or have a distinct external duct, I cannot say. 
The vessels separate, and one runs up on each side of the 
body towards its oral side (fig. 2). Arrived at the level of 
the pharyngeal bulb, each vessel divides into three branches 
(fig. 3) ; one passes over the pharynx and in front of the pha- 
ryngeal bulb, and unites with its fellow of the opposite side, 
while the other two pass, one inwards and the other outwards, 
in the space between the two layers of the trochal disc, and 
there terminate as coeca. Besides these there sometimes 
seemed to be another branch, just below the pancreatic sacs. 
A vibratile body was contained in each of the coecal 
branches ; and there was one on each side in the transverse 
connecting branch. Two more were contained in each lateral 
main trunk, one opposite the pancreatic sacs, and one lower 
down, making in all five on each side. 
* M. Udekem (Annales des Sciences, 1851) lias given a very elaborate, 
but I think not altogether correct, account of the water-vascular system 
of Lacinularia. He says that a vascular net- work exists at the base of the 
lobes of the wheel-organ ; that these unite into gland-like ganglia (my 
" vacuolar thickenings," in the margin of the disc infra) ; that from these, 
vessels proceed to the central glands (vacuolar substance, in which the 
" hand" of the water- vascular system terminates, milii), from which three 
great vessels are given off. Of these, one " passes above the digestive 
tube, and anastomoses with its fellow from the opposite ganglion ; the 
second presents the same disposition as the first, but is placed below the 
digestive tube ; the third passes directly downwards, skirting the digestive 
tube." M. Udekem found it "impossible to trace it any further, but 
considers that it becomes lost on the digestive canal and ovaries." He, 
therefore, has missed the external opening of the water-vascular system. 
What I have seen and described as "vacuolar thickeniiigs " in the 
peduncle, are described by M. Udekem as vascular ganglia, from which 
anastomosing vessels proceed. 
As M. Udekem's instrument does not seem to have been good enough 
to define the vibratile cilium — for he speaks only of a " vibratile or trem- 
bling movement" — I venture to think that he has been misled in describing 
these threads and vacuolar thickenings as forming any part of the true 
vascular system, 
Leydig'KS opinion of M. Udekem's results is, I find, much the same as 
my own. He says, " Critically considered, then, we find that Udekem's 
vascular system in Lacinularia is compounded of a multitude of the most 
heterogeneous parts of the animal — of structures which belong to the most 
different systems of organs, without one being a true blood-vessel." — L. c, 
p. 465. 
