THE TREMATOD A. 59 



exactly ; but that tliey do so for a long time, not many 

 weeks only, but for many months, I will hereafter prove. 

 I A\ill here only state that the above observations on the 

 CercaricB and their pupce were made in the months of 

 July and August, and that during this time, even when I 

 met mth individuals which had assumed the pupa state 

 at an earher period, there could not be discovered the 

 slightest difference between the larvce taken from the 

 pupa cases, and those which had become pupce a short 

 time before, so that it might be supposed that a stul 

 longer time was required before they would escape from 

 their cases. The same conclusion resulted from observa- 

 tions repeated in September. 



The first sign I observed of the animal quitting its 

 pupa case was in January, in some snails which I col- 

 lected by degrees from a ditch, where in the autumn I 

 had remarked a great number of CercaricB. These snaus 

 I had placed in vessels in a warm room. I had pre- 

 viously observed in various jö«^<^ that the larva contained 

 in them was a Httle changed ; for if I caused one of the 

 pupa cases to burst, by sudden compression between 

 glasses, a convoluted animalcule escaped from it, which 

 had the form of a Distoma (fig. 8 ß,) with a very promi- 

 nent acetabulum under the abdomen, and a number of 

 pointed spines situated on the upper surface of the collar. 

 At first the creature gave but little sign of life, and bent 

 itself slightly on all sides, but afterwards stretched itseK 

 straight out, and commenced very lively movements. 

 The figm:es 8 (5, 8 c?, and 8 d, exhibit this Distoma or 

 fluke, as I observed it many times in the winter months, 

 either immediately beneath the skin or in the water pas- 

 sages near the skin in the Limnceus stagnalis, many hun- 

 di'eds of which I kept in large vessels. Fig. 8 h still 

 exhibits the circlet of spines, from which it would seem 

 the animal had but just escaped from the pupa case. 

 The fissm^e in the middle of the collar on its abdominal 

 aspect, and the spines which in the neighbourhood of the 

 fissure cross each other, were very distinctly seen; at 



