
AILMENTS AND DISEASES 

Probably the most frequent forms of Cestode parasites are Schistoceph- 
alus solidus and allied species, which occur in many freshwater fishes in 

FIG. 87 Stickleback affected with Schistocephalus solidus; showing enlargement of side and abdomen. 
Slightly enlarged. 
immature forms. Figs. 86, 87 and 88. As adults they have fish-feeding 
birds and mammals as hosts. 

FIG. 89 Ascaris acus, a Nematod 
parasite. 1. Immature forms, enlarged. 
2. Subsequent adult form, enlarged, 

FIG. 88. Section of a Stickleback, 
showing cysts of Schistocepha/us solidus. 
Slightly enlarged, 
Nematopa or Rounpworms. ‘This group comprises the round 
and thread worms. They include a large number of families which occur 
abundantly in all genera of the Vertebrates and are more numerously and 
uniformly distributed than the individual members of the other parasitic 
orders. They have not apparently had the attention of Helminthologists 
that has been given to many other groups and the literature is fragmentary 
and widely scattered. Mention will here be made of the six principal 
families and the more generally distributed species. 
ASCARID AND CHEIRICANTHID#. ‘These parasites inhabit higher 
Vertebrates, principally birds and mammals, but two Nematods, bearing 
close resemblance to Ascaris teniussima, have been found in Western 
trout. Ascaris acus in the adult form is encysted in the intestines of pike, 
bass and trout, Fig. 89. Its immature existence is spent in the minnow, 
dace and other Cyprinide and with them is introduced into the subsequent 
host. 
CucuLttanip#&. Several species of these parasites occur in freshwater 
149 
