THE TREMATOD A. 79 



the anterior edge of the animal, and a delicate canal 

 passing doT\ai from it to the central lobe. 



Besides these, I clearly distinguished a tolerably large 

 double organ {cV, fig. 4/, and 4^,) the two branches of 

 which, proceeding from the anterior extremity of the 

 animal, and passing in a curved direction around the 

 stomach, unite in the mesial line behind the acetabulum, 

 and appear to be connected with a rounded swelling, 

 which is seen like a circular clear spot in front of the 

 horseshoe-like outlines of the posterior borders of the 

 animal. The situation would render it not improbable 

 that this double organ is connected with the function of 

 reproduction. 



The animal does not appear to creep out of the pupa 

 case through any regular opening, for close to the indi- 

 viduals above referred to as having just left the pupa 

 cases, I observed the latter irregularly crumpled up, and 

 scarcely recognizable. Fig. 5 a represents an animal 

 newly escaped from the pupa case ; several of its internal 

 organs were still apparent for the first hour or two 

 through the integument ; its changed condition, however, 

 afterwards prevented their being distinguished. The 

 organs marked s, t, u, v, are the same with those simi- 

 larly lettered in fig. 4, and I suppose it is the same with 

 that marked aj, though I am unable, in the pupa, to dis- 

 cover a connexion mth the organ marked v., as in the 

 animal. The figures b ö c d, represent, for the purpose 

 of comparison, individuals which I obtained at the same 

 time from pupa cases, either by opening them or bursting 

 them by compression between shps of glass. They are 

 evidently true Distomata. The most important changes 

 which are observed during the growth of these animals 

 consist in the very powerful contraction of the body, the 

 shape of which changes from the broadly lanceolate which 

 it is normally, to an obovate or pyriform, in consequence 

 of the anterior extremity constantly increasing in breadth 

 (fig. 5 e / y). Simultaneously with this change of form, 

 the activity of the animal diminishes, and becomes at last 



