452 PARASITES OF ANIMALS 



parasites are firmly anchored within the pulmonary organs is 

 quite another matter. 



As remarked in my f Entozoa/ the trematodes display a great 

 partiality for batrachians, more than half a dozen different 

 species of fluke being known to infest the common frog. Flukes 

 are likewise tolerably abundant in the saurian and chelonian 

 reptiles. I regret that I cannot find space so much as to enu- 

 merate the species. As one would naturally expect, the frog 

 has been exhaustively anatomised and examined for entozoa, 

 and it was this creature that supplied Leuckart and Mecznikow 

 with the materials which led to their well-known discovery 

 and controversy respecting the development, dimorphism, and 

 parthenogenetic phenomena exhibited by Ascaris nigrovenosa. 

 I cannot give the facts in detail. Female examples of the worm 

 live in the lungs of the frog. Their young, as embryos, pass 

 into the damp earth and mud, where they grow up into 

 sexually- mature forms different from the parent worms found in 

 the frog. These free adult worms, male and female, produce 

 rhabditiform embryos which present characters of their own 

 and attain a certain stage of growth. At this stage they 

 are conveyed into the lungs of the frog where they arrive at 

 sexual maturity. As there are no male worms in the frog, it is 

 probable that the embryos of these parasitic females are agamo- 

 genetically produced by internal budding, the sexual influence 

 of the free males being, as it were, continued onward without 

 actual contact with the parasitic females. Amongst the 

 interesting parasites of the frog one must also mention Amphi- 

 stoma subclavaium and Polystoma inter gerrimum. The former 

 worm resides in the large intestine and the latter in the urinary 

 bladder. The larvas (Cercaria diplocotylea) of this amphistome 

 reside in or upon the body of water-snails, and, like the 

 cercarian larvae of polystoma, they are furnished with eyes. I 

 state this fact on the authority of Pagenstecher ; and, since I 

 cannot devote a special section to the entozoa of mollusks, 

 I repeat, in part, the valuable results which Pagenstecher 

 published many years back and which have a permanent value 

 in relation to the origin of parasitic diseases resulting from 

 flukes. In the memoir quoted below, Pagenstecher gives the 

 following conclusions (Schlussbemerkungen) : 



" (a). The eggs of the trematoda vary in respect of size, 

 form, and color, being either furnished or not with a lid, and 

 accordingly distinguishable. In the mature condition they 



