DISEASES PRODUCED BY CYSTICA. 77 



helminthologists have long ago observed that certain species 

 inhabit and attain sexual maturity in the most different kinds of 

 birds and fishes. The conditions of life of the five races of 

 degenerated Teenies serratai (with their various oedematous forms of 

 scolex, which are also to be considered as varieties of race), were 

 certainly originally more simply and sharply defined, and must 

 have gradually become impressed with their present complex and 

 indefinite character from the domestication of the animals they 

 infest. 



At the same time, the results of these feeding experiments, 

 which I have just cited, contradict the belief that the cysts of 

 these worms have a physiological, 1 and not a pathological signifi- 

 cation, for all the Cystica mentioned are produced from a single 

 species of tape-worm, namely, the Taenia serrata, and it only 

 depends upon the nature of the spot to which these embryos 

 have been transplanted after having completed their immigration, 

 whether they degenerate into Coenurus cerebralis, or Cystictrcus 

 pisiformis, or tenuicollis, &c. When subject to the same external 

 influences, these degenerations will always present the same form ; 

 whence it seems justifiable to compare these continually recurring 

 and sharply-marked modes of degeneration of certain intestinal 

 worms with the phenomena of race. 



5. ON THE DISEASES PRODUCED BY CYSTIC WORMS, AND THEIR 



PREVENTION. 



After having pointed out, in the introduction, that all the 

 intestinal worms reach the interior of their hosts by immigration, 

 and after having shown by the feeding-experiments, that certain 

 cystic worms are transformed in the digestive canal of dogs into 

 a particular kind of tape-worm, I may be allowed to draw the 

 conclusion that, reversing the circumstances, the young of these 

 tape- worms may, by the help of the alternation of generations 

 which I have already described, be developed into cystic worms, 

 the species of the animals and also the nature of the organs, into 

 which the immigration takes place, exercising a specific influence 



1 Kuchenmeister has taken much pains of late to defend this view, in opposition to 

 mine, and has been led away by his zeal, to depart from that calmness of tone which 

 becomes scientific controversy. 



