204 ANIMAL PARASITES AND MESSMATES. 



by side the cercaria of this amphistome, and the adult 

 and sexual amphistome, as it is found in the intestines 

 of the frog. 



Constantine Blumberg has recently published an 

 interesting memoir on the structure of the Amphistomum 

 conicum. 



A beautiful trematode worm, known by the name 

 of Hemistomum alatum, whose antecedents have not been 

 ascertained, lives usually in the intestines, of the fox. It 

 is about four or five millimetres in length (about - 17in.). 

 Many birds harbour Holostomes which belong to the 

 same group, the first state of which is not yet known. 

 The Holostomum macrocephalum is common in the intes- 

 tines of rapacious birds ; it is from five to seven milli- 

 metres in length (about "23 of an inch). 



We close the history of trematode worms by giving 

 the figure of a beautiful one known under the name 

 of Polystomum, which fives in its adult state in the 

 bladders of frogs (Fig. 48). Interesting observations 

 have recently been made on the manner in which they 

 are introduced into the bladder. 



The worms which naturalists call Cestoids, or Cestodes 

 (which means, like ribbon or tape), have for their type 

 the tape-worm known by every one. They are very 

 abundant in many animals, are found in almost every 

 class of the animal kingdom, and are almost as common 

 as the distomians, of which we have just spoken. They 

 are introduced into animals which' are vegetable-feeders, 

 by means of water and plants, and into carnivorous 

 animals by their prey. The tape-worms of the herbivora 

 lay eggs like the others, but their embryos have, as soon 

 as they are hatched, a ciliary covering which allows them 



