32 THE TAPE-WOEM. 



and entering uninjured into the intestine of its new owner, 

 arrives at sexual maturity. The extent of development in each 

 individual will be found to be in proportion to the time it has 

 passed in the bird's alimentary canal after its passive emigration. 

 Since the connection between Bothriocephalus solidus and nodosus 

 has been known, helminthologists have ceased to regard these 

 two taenioid worms as different species, but in accordance with 

 the suggestion of Dr. Creplin, who first drew attention to the 

 relationship between them, they have been considered to be 

 different stages of the same species, Schistocephalus dimorphus. 

 A similar instance occurs in the case of the Ligula simplicissima, 

 infesting the abdominal cavity of various species of carp, whose 

 sexual organs are, and remain, undeveloped, as long as the worm 

 remains within the fish, whilst when the latter is eaten by, and the 

 entozoon thereby conveyed into the intestines of, ducks, divers, 

 waders, and other water-fowl, it attains perfect sexual develop- 

 ment. In the older helminthological systems the sexually ma- 

 tured Ligula simplicissima is described under various specific 

 names, sometimes as Liyula sparsa, uniserialis, sometimes as 

 Ligula alternans, or interrupt a. 



Many Cestoidea, during their youth, lodge in the liver and 

 peritoneum of fishes. In these organs they excite a morbid 

 exudation whereby a membranous substance is produced, which 

 forms a kind of capsule round the worm, and thus, as it were, 

 excludes it from the organism. This act, by which the organs 

 seek to free themselves from such unwelcome guests, I shall 

 designate by the name of " extrinsic" 1 encysting process already 

 given in page 25. 



The encysted Cestoidea increase in size, but do not become 

 sexually mature, from the absence of the conditions necessary 

 to the attainment of this state ; and should their hosts perish 

 without having been devoured by an animal of prey, the sexless 

 Cestoidea will die with them, without leaving any progeny. 

 Various examples illustrate the truth of this statement. 



Mention has already been made (at page 29) of the Triaeno- 

 phorus nodulosus which infests the intestine of the pike and 

 the perch, where alone it is to be met with sexually mature. 

 Helminthologists, however, give other localities of this worm, as 



1 I have added the word " extrinsic" here to distinguish this from the self-encysting 

 process by exudation from the entozoon itself. [ED.] 



