88 DEVELOPMENT OF 



However, in order that the observation that the species 

 of Distoma which is developed from the larva of Cercaria 

 echinata does not attain its complete form till the third 

 generation, should not stand alone and unsupported by 

 analogy, I will state some observations on another species 

 of Cercaria, although it must be done with great brevity, 

 and I am not able to give any figures illustrating their 

 development. 



Cercaria ephemera (Nitzsch) was the first species of 

 Cercaria intimately known to naturalists, and indeed only 

 through Nitzsch' s curious observations of the phenomena 

 attending their becoming pupce. More lately, Baer so 

 commonly noticed their pupcB in the auricle of Paludina 

 vivipara (without, however, knowing any more than 

 Nitzsch, that they were iQd^y pupcB,) that he termed them 

 a species of Cercaria peculiar to the auricle ; and Siebold, 

 (1. c.) has again observed and described them in ihepupa 

 state. ' I also have had several opportunities of becoming 

 acquainted with them, and will only add as regards these 

 animals themselves, that I have obtained several Distomata 

 from the liver of Paludina vivipara, which from their 

 external form I am compelled to regard as the species 

 into which the Cercaria ephemera is metamorphosed from 

 the pupa ; however, the want of individuals newly come 

 out of this state, prevents proof of this assertion being 

 given. The " nurses' of this species have, on the con- 

 trary, as far as I know, been described only by Siebold, 

 and as far as my observations themselves extend, they 

 correspond with those of that helminthologist ; they may 

 for instance be compared with the " nurses' of Cercaria 

 echinata; like them they are elongated, cylindrical ani- 

 malcules, having vermicular motion; they have a well- 

 marked muscular mouth; and a very long and wide 

 digestive cavity, which causes a protuberance in the middle 

 of the animal, and reaches even to its posterior extremity; 

 it has no lateral processes. The Cercaria ephemera lies, 

 in all stages of development, between the digestive cavity 

 and the skin, but never in great numbers ; as soon as it 



