Larval Trematodes. 245 



body and measures '194 mm. The suckers are thus nearly 

 equal, although in the adult the ventral sucker is considerably 

 larger than the Dial sucker. The greater relative increase of 

 the ventral suckei-^ however, is of almost invariable occurrence 

 amongst Distomids. 



'J he internal anatomy conforms very well to the Stephano- 

 chasmus type. The pear-shaped pharynx measures •14 X 

 '09 mm. ; the prepharynx is twice as long and the oesophagus 

 half as long. The excretory vesicle, as commonly occurs in 

 encysted cercarise, is of disproportionately large size. The 

 testes are rather near the posterior end and the ovary is a 

 little in front of them. The cirrus-pouch is well formed and 

 extends to midway between the ventral sucker and the ovary. 

 The yolk-glands were not very distinct. 



The identitication of larval Stephanochasmus species would 

 a]>pear to rest very largely on the number and relative length 

 of the cephalic s})ines. Other features which aid in 

 identifying adult species, such as the size of the suckers, the 

 length of the cirrus-pouch, and the extent of the yolk-glands, 

 are of very doubtful value in the case of cercarise. The yolk- 

 glands are not, as a rule, conspicuous enough, while the great 

 increase in the length of the post-acetabular relatively to the 

 pre-acetabular region as the genital glands develop and the 

 cercaria attains maturity renders futile any differentiation 

 based on the comparative sizes of the suckers or the pro- 

 portionate length of the cirrus-pouch. Assuming, however, 

 that the number of cephalic spines is constant, or very nearly 

 so, in each s])ecies, it is obvious that this would provide a 

 fairly reliable test in diagnosing species, except such as possess 

 a nearly equal number of spines. 



Of the known species of Stephaywchasmiis, St. cesticillus 

 (Molin), St. hicoronatus (Stoss.), St. p7istis (Deslongch.), 

 St. mimdiis, Lss., and iSt. rhomhispinosus, Lebour, have ail 

 less than 40 cephalic spines. In St. caducus, Lss., there are 

 48, in St. triglcB, Lebour, about 50 (?), and in St, baccatus, 

 i^icoll, 5G, It seems hardly likely that the cercariae of 

 St. caducus and St. baccatus could be confused, for not only 

 is there a diflFerence of 8 spines, but the anterior row con- 

 tains the longer spines in St. caducus, while the reverse is 

 the case in St. baccatus. At the same time it must not be 

 forgotten that it is often a matter of great difficulty to deter- 

 mine the length of the spines accurately, for owing to the 

 curvature ot the surface on which they are set they are 

 usually seen somewhat foreshortened, and this aj^plies more 

 particularly, to the spines of the anterior row. Between 

 St. iriyloi and St. baccatus there is greater difficulty iu 



