54 CYSTICERCUS FASCIOLAETS. 



It is to the peculiarity in the form of the Cysticercus fascio- 

 laris that we owe the recent recognition of the connection 

 between the cystic and the cestoid worms. The similarity of the 

 head of this Cysticercus with tjjat of the Tcenia crassicollis is so 

 great and striking, that I can scarcely claim much merit for 

 having been the first to entertain the idea which I thus ex- 

 pressed i 1 the Cysticercus fasciolaris is nothing more than a 

 strayed or degenerated Tcenia, which may, however, attain the 

 normal form of a tape-worm if transported to the intestinal 

 canal of a suitable animal. Both forms are so intimately related 

 to each other in form and organization, that I am not surprised 

 at Allen Thomson, of Glasgow, having recognised the agreement 

 of the Cysticercus fasciolaris with the Tcenia crassicollis without, 

 as it seems, being aware of my researches and publications upon 

 the subject. 2 The mutual affinities and relations of these two 

 Entozoa are the more perceptible, because during the growth of 

 the Cysticercus fasciolaris the joints of the future tape-worm are 

 developed between the caudal vesicle and the head. These joints 

 certainly remain narrow, and develop no sexual apparatus, but 

 they give to the scolex, which in this stage of development 

 always has the head extruded, such a characteristic appearance, 

 that its identity with the Tcenia crassicollis can only be denied by 

 those who regard the caudal vesicle as the sole test of sys- 

 tematic position. If we examine the Cysticercus fasciolaris or 

 altered Tcenia crassicollis, more narrowly, we shall perceive in this 

 tape- worm the same peculiarity which occurs in the various other 

 cestoids, for instance, in Tricenophorus nodulosus, Tcenia longicollis 

 and ocellata, viz., that the body of the tape-worm grows from 

 the back part of the head and neck of the scolex, even before 

 this has reached the intestine of the vertebrate animal adapted to 

 its sexual development (see page 32). There is, however, an 

 additional departure from the ordinary course in the Tcenia cras- 

 sicollis, that during the development of its scolex its receptacle 

 undergoes a dropsical degeneration. 



As the Cysticercus fasciolaris, which is found always encysted, 

 in the livers of various rodents most commonly those of rats 

 and mice is often met with several inches long, the caudal 

 vesicle terminating the elongated body of such individuals, which 



1 Compare my article " Parasiten," 1. c., pp. 650, 676. 

 3 'Zeitschrift fiir Wiss. Zoologie/ Bd. iii, 1851, p. 97. 



