491] LARVAL TREMATODES—CORT 45 



tended and contracted their bodies rapidly, the preacetabular region 

 being the most active, but they were unable to swim. The tail, bent 

 ventrad and pushing against the substratum, aided somewhat in loco- 

 motion, and at times the oral sucker was used for attachment. By this 

 peculiar method the animal was able to make a little progress with a 

 great deal of effort. Leuckart (1886:86) notes the same type of move- 

 ment for Cercaria limacis Moulinie, a stumpy tailed cercaria from Limax 

 cineria. 



"Ausser Stande zu schwimmen, benutzen diese Wurmer den fast 

 hertzf ormigen Schwanzanhang beim Kriechen als Nachschieber. 

 Some of these cercariae were kept alive and active in tap-water for 

 three or four days. 



Cercaria trigonura (Figs. 48, 50) has an elongate, cylindrical body, 

 averaging in mounted specimens 0.24 mm. in length and 0.06 mm. in 

 width. The oral sucker measures on the average 0.049 mm. in length 

 and 0.039 mm. in width and the acetabulum which is slightly back of the 

 center of the body is smaller, being 0.04 mm. in diameter. The cuticula 

 is thin and at the anterior end beset with tiny spines, which are numer- 

 ous over the oral sucker, thin out posteriad and disappear entirely back 

 of the pharynx. 



The tail of Cercaria trigonura is short, easily detached, grooved 

 ventrally, and has the extremity bluntly pointed (Figs. 48, 50). It 

 has an average length of 0.052 mm. and a width of 0.024 mm. Under 

 the cuticula is a thin layer of circular muscles which are supplemented 

 ventrally by a number of stronger longitudinal fibers that extend from 

 the base to the tip. The size of these strands and the fact that they 

 have no opposing muscles on the dorsal side would account for the 

 fact that the tail is usually bent ventrad. The bulk of the tail is formed 

 of loose parenchymatous tissue consisting of scattered nuclei, connecting 

 protoplasmic strands and good sized vesicles. 



On the ventral surface of Cercaria trigonura just at the base of 

 the tail is a slit-like opening, which extends forward a short distance 

 and dorsad reaches up into the body. Opening into this cavity are 

 large numbers of unicellular glands which stain very heavily with 

 haematoxylin. Figure 48 pg shows the relation of this posterior glandu- 

 lar structure. It is interesting that the shape and position of the tail 

 give it the appearance of a short trough ready to carry off the secre- 

 tions of this gland. The position and structure of the posterior gland 

 suggest that it may function for adhesion. No activity which suggests 

 such a function has been observed and for none of the other stumpy 

 tailed cercariae has the description of a posterior glandular structure 

 been found. 



