GIGLIOL1, ON THE GENUS CALLIDINA. 241 
digestive tube itself; as indigo swallowed, diffused itself 
throughout this mass: while I am positive that a distinct 
alimentary canal exists, as I have above described ; at any 
rate, such is the case in C. parasitica, in which its walls are 
so tenacious that, having crushed accidentally one of these 
creatures, I had the pleasure to see nearly the whole alimen- 
tary canal float out free and disengaged from the granular 
mass which invests it, through the ruptured integuments. 
No so-called salivary or pancreatic glands exist, and the 
substance surrounding the digestive tube is one homogeneous 
cellulous mass, of a yellowish-green colour, and even with the 
highest magnifying powers I could detect no follicules or coecee 
in its substance. 
Water-vascular system.—This consists of a large, irregular, 
rounded vesicle, situated on the ventral side of the cloaca 
(fig. 2) ; it contracts rhythmically at regular intervals (about 
30”); I could find no communication between it and the 
cloaca, or any special outlet of its own. Running into it, 
about its middle, are two extremely small, convoluted water- 
vessels, which run up along the sides of the body. I have 
traced them till under the trochal disc, in which I suppose 
they terminate ceecally. Even with one of Smith and Beck’s 
largest first-class microscopes, with a linear power of 1300 
diameters, I could make out no transverse branches or vi- 
bratile bodies, though they exist, no doubt. In fig. 2 the 
water-vessels are represented considerably larger in propor- 
tion than they really are. 
Nervous system and sense organs.—Just beneath the trochal 
disc, on the left side of the ventral aspect of the buccal funnel, 
I saw in several individuals a small mass, which may be the 
ganglion, though I will not be sure about it. I could make 
out no ramifications proceeding from it, neither could I make 
out anything corresponding to the ciliated fossa. 
The calcar (fig. 5) is large and well developed; it is not 
ciliated at its extremity (at least, with very high powers I 
could detect no such thing), but trilobate, the external lobes 
being more or less elongated. It is constantly protruded, 
feeling around, and is, beyond a doubt, a tactile organ. 
When the creature is contracted it appears on the median 
line (fig. 4), and when the trochal disc or proboscis is ex- 
tended it generally appears on one side (fig. 2); it is rarely 
retracted as in fig. 1. No eye-spots exist in young or adult ; 
and Mr. Gosse has observed that his C. didens thrives well 
in the dark, but when exposed to a strong light it soon dies ; 
this is very interesting, for many other animals are in the 
same predicament, and C. parasitica, living on G. Pulex and 
