94 ANIMAL PAltASITES. 



■worm, and according to the different hosts (cold or warm-blooded), 

 sometimes the form of a globular vesicle, sometimes that of a flat, 

 band-like strip, and sometimes is only just sufficient to cover the 

 scolex, lying quite close upon it, when it really forms nothing but a 

 receptaculum capitis. Thus we obtain three forms allied to each 

 other in their degree of development ; — the cysticercal forms 

 {Vermes cystici, including Ccenari and Ecldnococci) ; the platycercal 

 (similar to Stein's cestoid worm of Tenebrio molitor, and Yon 

 Siebold's from Arion empiricorum) ; and the acercal (certain 

 embryos of Tetrarhynchi). Every one of these is a normal form; 

 even the cysticercal forms are neither morbidly degenerate, nor 

 become dropsical, nor strayed. The formation of vesicles is settled 

 by the species of worm, and by the animal infested (warm-blooded). 

 The species of cystic worms have never yet been found in any 

 animal without the vesicular structure, and in an acercal or 

 platycercal state the caudal vesicle does not occur in the very 

 succulent forms living in cold-blooded animals, from which the ces- 

 toid worm can constantly and readily derive fluids. As was known 

 by Goeze, the caudal vesicle is a reservoir of nourishment. The 

 embryos of all the Cestodea which pass through a vesicular state 

 are extraordinarily small, possess very small embryonal hooks, 

 and are enclosed in brownish yellow envelopes, which are uneven 

 externally. All three forms are undeveloped immature forms, 

 and must therefore be struck out .of the system as genera, and 

 further must be arranged with the Cestodea. 



IV. The resting scolex transferred into the intestine of an 

 animal becomes converted into the scolex jwssing into activity. 

 The latter is distinguished from the resting scolex by the extension 

 of the entire body by the altered position of the adherent 

 apparatus (suckers and hooks), by the attachment in the intestinal 

 canal, and in the cysticercal and platycercal forms by the casting 

 off of the barren portion of the embryonal vesicle and the 

 formation of a cicatrix on this spot. In the acercal forms nothing 

 is cast off', nor is there a cicatrix-formation. 



V. The strobila = the tape-worm colony, budding immediately 

 from the scolex which has become active, by asexual propagation 

 (gemmation) is more or less distinctly jointed, and becomes sexually 

 mature posteriorly. Its last segments, which are cast off and lead 

 an independent existence, are called proglottides (I), and bear 

 within them the embryos produced by sexual reproduction (II). 1 



1 Appendix A. 



