240 GIGLIOL1, ON THE GENUS CALLIDINA. 
about ,1,th of an inch in length and ;2,,ths of an inch in 
breadth. 
Muscular system.—On compressing the animal suddenly 
and violently, I saw several longitudinal and some transverse 
muscles (fig. 2), which were certainly not striated. Other 
muscles also exist, and often the tissues under the external 
integument contract within it, forming a sinuous outline, 
very likely under muscular action (fig. 1). 
As in all Philodinade, the trochal disc is double, or rather 
bilobed ; it is small, and surrounded by a single circlet of 
short cilia (fig. 2); it is rarely extended, the cilia continu- 
ally vibrating, even when it is retracted. In small individuals 
the trochal disc is about —-4,,ths of an inch across. 
Digestive system.—In the middle of the trochal disc, on 
the ventral side, is a ciliated, protrusible, wedge-shaped pro- 
boscis, having at its extremity the oral aperture; it is not 
thick and rounded, as described by Mr. Gosse in C. bidens, 
and it never projects when the trochal disc is extended. The 
oral aperture (fig. 3) leads into a long, narrow, buccal funnel, 
richly ciliated internally (fig. 3), and dilated in the middle ; 
it narrows again, and leads into the pharyngeal bulb or mas- 
tax, which is highly muscular, trilobate, and armed with a 
pair of moderately sized jaws, each possessing two teeth (fig. 
3). A short esophagus follows, leading into a large pyriform 
stomach (fig. 3), composed distinctly (as the rest of the in- 
testine seems to be) of two membranes, the inner one sup- 
porting numerous cilia; it gradually narrows into the intes- 
tine, which has a bend on the left if the animal is considered 
in its natural position (fig. 1) ; the mtestine gradually widens 
into a broad cloaca or rectum, richly ciliated, which opens 
externally on the left side of the dorsal aspect of the second 
segment of the tail (fig. 1) in a small anus, which is slightly 
protrusible, and not ciliated; the intestine also appears not 
provided with cilia. The particles of food are constantly 
undergoing a revolving movement in the stomach, as also 
the fecal granules in the cloaca. In a large specimen the 
total length of the alimentary canal was 1th of an inch; the 
pharyngeal bulb was ,4,th of an inch in length and +3,,ths 
of an inch broad ; the cesophagus was -,),,th of an inch long ; 
the stomach -—3,,,ths of an inch in length; and the intestine 
was ~;'5,th of an inch in breadth. 
Now, Mr. Gosse* considers in C. bidens the whole mass 
surrounding the alimentary canal, from beneath the mastax 
to where the intestine dilates and forms the cloaca, as the 
* MSS., vol. iii, 1849, pp. 9—81, fig. 88 e. 
