CESTODES 187 



been included amongst the other intestinal worms, and Zeder (1800) 

 established a special group (cystici) for them. Things remained in this 

 condition until the middle of the last century, when Kuchenmeister, 

 by means of his successful feeding experiments, demonstrated that the 

 cysticerci were definite stages of development of certain tapeworms. 

 Before Kuchenmeister, E. Blanchard, van Beneden, and v. Siebold had 

 held the same opinion in regard to other asexual cestodes. 



Since the most remote period another question had occupied the naturalists 

 again and again, the question of the morphological nature, that of the 

 INDIVIDUALITY OF THE TAPEWORM. The ancients, who were well acquainted 

 with the proglottides that are frequently evacuated (Vermes cucurbitani\ were 

 of opinion that the tape-worm originated through the union of these separate 

 proglottides, and this view was maintained until the end of the seventeenth 

 century. In 1683 Tyson discovered the head with the double crown of 

 hooks in a large tape-worm of the dog ; Redi (1684) was a l so acquainted 

 with the head and the suckers of several Taeniae, and Andry (1700) found 

 the head of Tcenia saginata, Bonnet (1777), and Gleichen Rusworm (1779) 

 found the head of Dibothriocephalus latus. Consequently most authors, on 

 the ground of this discovery, considered the tapeworm as a single animal, 

 that maintains its hold in the intestine by means of ' the head, and like- 

 wise feeds itself through it. The fact was recognised that there were 

 longitudinal canals running through the entire length 'of the worm, and it 

 was thought that these originated in the suckers ; and naturalists regarded the 

 entire apparatus as an intestine. As it was found, moreover, that the joints 

 form at the neck, and are^cast off from the opposite extremity, the tape- 

 worm was also compared with the polyps, which were formerly regarded 

 as independent beings. 



Steenstrup, in his celebrated work on the alternation of generations 

 (1841), was the first to inaugurate another stage of advance. His studies 

 were followed still further by van Beneden, v. Siebold and Leuckart, and 

 until a few years ago all authorities adopted his views. Accordingly, the 

 tapeworm is composed of numerous individuals, something like a polyp 

 stem, and, in addition to the proglottides the sexual individuals which are 

 usually present in large numbers there is ONE individual of different struc- 

 ture, the Scolex, which not only fastens the entire colony to the intestine, 

 but actually produces this colony from itself, and therefore is present 

 earlier than the proglottides. The scolex is 'a nurse which, though itself 

 produced, by sexual means, increases asexually like a Scyphistoma polyp ; 

 the tapeworm chain has, therefore, been termed a Strobila. Consequently 

 the development of the tapeworms was explained by an alternation of genera- 

 tions. In support of this opinion it was demonstrated not only that the 

 adult sexual creatures, the proglottides, can separate from the colony and live 

 independently for a time, but that in certain TaBniae, and especially in many 

 cestodes of the shark, the proglottides detach themselves long before they have 

 attained their ultimate size, and thus separated continue to develop, grow and 

 finally multiply ; the scolex also exhibits'" a certain independence in so far as, 

 though not, as a rule, capable of a free life, yet in some cases lives as a free being, 

 partly on the surface of the body of marine fishes and partly in the sea. With the 

 more intimate knowledge of the development of the cysticerci, the independent 

 nature of the scolex was recognised. It is formed by an invagination of the 



