270 ANIMAL PARASITES. 



the excretory organ, which is filled with globules, emits regular 

 transverse branches over the sucking disc. 



In order to determine the mutual relations of the Cercarice, 

 enclosed and tailless Cercaricp (young trematode larvse), and 

 mature Trematoda, we have as data, as in the Cestoidea, in the 

 armed species the spinous ring and the anterior part of the head, 

 in the unarmed the simple boring spine in the same spot and 

 the dilatation of the intestine. According to De la Valette's ex- 

 periments, it is certain that the Cercaria echini/era is converted, 

 very rapidly in the intestine <Jf warm-blooded animals, and 

 slowly in cold-blooded species, into D. echini/era (Val.) ; that Cere, 

 flava of the Ephemera becomes transformed into Monostomum 

 flavum of the finches and sparrows ; but that C. echinata is con- 

 verted into D. echinata Anatis Boschadis (Zeder.) 



From these experiments we also see, when we run through the 

 animals experimented upon by De la Valette, which are partly 

 cold-blooded, and partly warm-blooded animals (e. g. Coluber 

 natr'ix, Rana temporaria, Fringilla domestica and F. montana, 

 Columba domestica, and Lepus cuniculus), that the diffusion of the 

 Trematoda in the animal kingdom is by no means confined within 

 such narrow limits as that of the Cestoidea. 



If we apply what has thus been established by experiment, per 

 analogiam to Distomum hepaticum, the following may appear to be 

 most probable with regard to the mode in which the Distoma 

 reach the liver of man, and domestic animals of the classes 

 Herbivora and Omnivora. Although it is still unknown to us 

 how the embryo becomes metamorphosed, and into what Cercaria- 

 sacs or Redia it is converted, and where these Cercaria-sacs or 

 Redice live ; although we do not know whether the brood of D. 

 hepaticum is tailed or tailless, and where it encysts itself, whether 

 free in the water in the manner of Monostomum, in aquatic mol- 

 lusca or insects, or in higher animals which occasionally visit 

 stagnant waters yet there is much probability that the herbivorous 

 or omnivorous domestic mammalia infect themselves with free 

 encysted young Distoma either by devouring snails which adhere 

 to the grass of the meadows, especially in moist pastures, or by 

 drinking from impure, stagnant waters (marsh or pond water). 

 Exactly the same thing would then take place in man, by means 

 of snails adhering to salad, fallen fruits, radishes, turnips, and 

 other roots. Nay, such small snails might even be introduced 

 with dry fodder into the stomachs of our domestic animals during 



