82 ANIMAL PARASITES. 



scolex bears behind it the middle-body, and the caudal vesicle on 

 a fine filament, (that is a rudimentary transverse fold, or so- 

 called segment). Nothing more than the scolex-head and neck 

 of the third stage of development remain, and these alone are 

 transferred into the new one. The length of the remaining 

 parts varies, first with the different species, and then with the 

 various individuals of the different species, according to the 

 duration of their existence in the vesicular stage, and according 

 to the length which their neck had attained during this stage. 



On the abdominal extremity of the Cestoid worm, which is 

 now, after casting off the body, greatly shortened, we now see 

 shreds and flakes hanging, together with a funnel-shaped con- 

 striction. These are the rudiments of the receptaculum capitis, 

 which was also extended during the changing of the Cysticercus 

 which has become a Tcenia, and formed the boundary between 

 the head and body. A portion of this receptaculum is then 

 always cast off with the body and the caudal vesicle, and a 

 portion wraps itself into the funnel-shaped constriction of the 

 young Tcenia. The shreds remain for two days, and then a 

 cicatrized notch is observed. It leads, according to Leuckart, 

 into a cylindrical cavity, passing through the whole body as far 

 as the rostellum ; its walls grow greatly, by which means the 

 scolex is converted into a solid and not inflated body. At various 

 times, sooner or later, according to the evolution and age of the 

 cystic worm, (in Cyst, pisiformis, for example, in two, or at 

 the utmost four days, but not as Lewald supposed in fourteen 

 days), the formation of segments commences, and with this, 

 consequently, this stage of development is concluded. 



I repeat here that Taenia cannot be reared from such scolices as 

 do not exhibit perfectly developed hooks. They die immediately. 



The first transformation of all cystic worms introduced into 

 the intestine of a warm-blooded animal takes place in the same 

 way, but the process stops before the commencement of segmen- 

 tation in those cases in which the intestine of the animal in 

 which the vesicular worm has arrived is unfavorable for it and its 

 further development. All the subsequent growth in this case 

 becomes an inarticulate, tail-like appendage, and such a Cestoid 

 worm in an unsuitable intestine remains stationary half-way 

 between the fourth and fifth stages of development. Moreover, 

 in this condition, it lasts only for a short time, and at the 

 end of a fortnight there is usually no trace of it to be found. 



