156 won MS. 



fishes. It is viviparous, but the embryo, before it 

 is extruded, itself contains an embryo, and this in 

 turn another, so that three generations of embryos 

 are represented simultaneously. 



Diplozoonparadoxum, consists of two individuals united. 

 The single embryo (Diporpa) is at first_ free- 

 swimming, but becomes a parasite on the gills of 

 the minnow, and there two individuals unite very 

 closely and permanently. 



Tristomum, with three suckers, is not uncommon on the 

 skin of some marine fishes. 

 Trematodes with indirect development — Digenetic. 

 e.g., Fasciola or Distomum. 



Bilharzia or Gyniecophorus htBiimtobius, a dangerous 

 parasite of man, widely distributed in Africa. It 

 infests the urinary and visceral blood-vessels. The 

 sexes are separate, and the male carries the female 

 inserted in a groove. 



Monostomum, a form with one sucker. 



Class Cestoda. Tapeworms, etc. 



The Cestodes are elongated flat worms, endoparasitic in 

 adult life. "With one exception the adults occur in the 

 alimentary canal of Vertebrates. 



In the simpler forms (Arckigetes, CaryophyllcBus, Am- 

 philina), the body consists of one joint, and has but one set 

 of (hermaphrodite) reproductive organs. In median types 

 {e.g., Ligula), there are several sets of reproductive organs 

 and hints of jointing. In the more familiar forms, such 

 as Tcenia and Bothriocephalus, there are numerous joints, 

 each with a measure of independence, each with a full set 

 of reproductive organs. 



An ordinary tapeworm stands in a certain sense between 

 unsegmented and segmented " worms," for while it has 

 numerous similar joints, these are not integrated into a 

 unified many-jointed organism. 



The life-history is markedly divided into non-sexual and 

 sexual stages, which, though not accurately comparable to 

 " alternation of generations," illustrate the same general 

 rhythm. 



Begin with a long tapeworm, pendent by its " head " from 

 the wall of the intestine. We may take the case of Tcenia 

 solium, one of the most frequent tapeworms infesting man. 

 The fixed " head," with four suckers and many hooks, has 



