AND THE LOWEE ANIMALS. 215 



of their followers, we are now in possession of a 

 general history of the development and migrations 

 of all these beings, which, though accepted hesi- 

 tatingly at first, must be more and more regarded 

 as truthful, in proportion as new facts are accumu- 

 lated. 



According to the Belgian naturalist, the Taenia's 

 egg produces a proto-scolex, which is a little animal 

 with an almost homogeneous body, in which it is only 

 possible to distinguish six hooklets, or rather six very 

 sharp spicules, arranged in three groups.* The two 

 middle ones form a sort of lancet, and perforate the 

 tissues placed in front of them ; the two lateral pair 

 pressing against the aperture thus formed, and working 

 backwards, send the embryo forwards, somewhat like 

 the manner in which a man employs his arms in hoist- 

 ing himself through a trap-door. The young cestoids 

 are urged forwards by an instinctive impulse. Many of 

 them perish on their journey, but some reach an organ 

 suited to their wants, and then they are transformed 

 into a vesicle, upon which are produced by genea- 

 genesis the heads of the Taeniae which are now so 

 many deutoscolices .f When the animal in which these 

 first phenomena have occurred, is devoured by some 

 other, the vesicle disappears, the taenia-heads are 

 isolated, and each of them develops from its posterior 



# Note on the Tcenia dispar and the mode in which the cestoid 

 embryos penetrate the tissues. — "Bulletin de l'Academie royale 

 de Belgique," 1854. 



f In this sketch of the development of cestoids, which for the 

 most part is deduced unquestionably from Yan Beneden's writings, 

 we have combined the results of his researches with those of 

 Kiichenmeister's. It was the latter who saw the vesicles which 

 are simple at first, give rise to the taenia-heads by gemination. 



