Phytogeny of 'the Organization of the Cestoda. 423 



flea, from which Tamia elliptica ( = cucumerina) of the human 

 intestine is derived. 



It is only recently that we have received full details 

 concerning this larval form and its caudal appendage, 

 through the observations of Grassi and Rovelli *. Both 

 of these authors recognized the soundness of the homo- 

 logy of body and tail-portion with the corresponding parts 

 of the Cercaria, though they perhaps went too far in inter- 

 preting the anterior invagination of the Cysticercoid as 

 the equivalent of the buccal cavity, the rostellum as the 

 everted pharyngeal bulb, and the body-cavity without suffi- 

 cient basis as the commencement of the mid-gut. 



In correspondence with this comparison we also have the 

 apparent agreement between the development of the Cercaria- 

 tail and that of the caudal portion of the Cysticercoid, which, 

 moreover, with reference to the position of the embryonic 

 hooks, had been regarded as the enlarged body of the hexa- 

 canth embryo, and accordingly styled u head-maker " (Kopf- 

 bildner), and explained as nurse of the presumably subse- 

 quently formed scolex. As a matter of fact, however, it by 

 no means represents the whole of the body of the embryo, 

 but only the smaller portion thereof, from which, just as in 

 the case of the cells budded off from the inner surface of the 

 Redia to form the Cercaria, a broader section is differentiated 

 as body and a narrower one as caudal appendage f. But 

 this establishes beyond a doubt the value as individuals of 

 the Cysticercoid and of the Cysticercus which is to be derived 

 from it, in opposition to that view which would see in the 

 Cysticercus a colony composed of at least two individuals, 

 namely of the embryo, metamorphosed into the caudal appen- 

 dage, or, rather, vesicle-wall, of the Cysticercus, and of the 

 Cestode-head or scolex subsequently produced from this by 

 budding. 



The changes experienced by the Trematode-larva in its 

 transition to the Cestode-larva also affect, in correlation to 

 the atrophy of the alimentary canal and the consequent 



* " Embryologische Forschungen von Prof. Battista Grassi und Dr. 

 Giuseppe Rovelli," Centralblatt fur Bacteriologie u. Parasitenkunde, 

 Cassel, 1889, v. Band, no. 11. 



t Grassi's observations on the development of the Cysticercoids of 

 Tcenia elliptica and murina have proved this deduction to be well founded ; 

 but in direct contrast thereto Yillot regards the caudal appendage of the 

 Cysticercoids as a new formation which has arisen from the embryo by 

 budding. He does not, however, establish his contention, which is also 

 directly opposed to the older view of the caudal appendage as the body 

 of the embryo. "Villot, " Memoire sur les Cysticerques des T^nias," 

 Annales de Sc. Nat. 1883, Tom. xv. 



