304 



THE ANIMAL PARASITES OF MAN 



turn form numerous scolices. Echinococcus-like conditions also 

 occur in cysticercoids, as, for instance, in those peculiar to earth- 

 worms ; and similar conditions prevail in a larval form known as 

 Staphylocystis, found in the wood-louse (Glomeris). Thus it happens in 

 these cases that finally one tapeworm egg produces not one, but 



numerous tapeworms, for, under 

 favourable conditions, each scolex 

 can form a tapeworm. 



FIG. 201. Section through a 

 piece of a Ccenurus cerebralis, 

 with four cephalic invaginations 

 in different stages of develop- 

 ment. At the bottom of the 

 invaginations the rostellum, hooks 

 and suckers develop. (From a 

 wax model.) 



FIG. 202. Median section through 

 a cysticercus, with developed scolex 

 at the bottom of the invagination. 

 (After Leuckart.) 



The rudiment of the scolex appears as a hollow bud, the cephalic invagination 

 usually directed towards the interior of the bladder cavity; on its invaginated 

 surface arise the four suckers, and the rostellum with the 

 hook apparatus is formed in its blind end ; we thus get a 

 Tnenia head, but with the position of the parts reversed 

 (fig. 201). In many cysticerci the head rises up from the 

 base of the cephalic invagination and is then surrounded by 

 the latter. A more or less elongated piece of neck also 

 develops, and even proglottids may appear, as in Cysticerctis 

 fasciolaris (the larva of Tcenia crassicottis of the cat) of the 

 Muridae, a process somewhat analogous to that of Ligula, etc. 



The period that elapses from the time of 

 infection till the cysticercus is fully developed 

 varies according to the species ; the cysticercus 

 of Tcvnia saginata requires twenty-eight weeks, 

 that of T. marginata seven to eight weeks, that 

 of T. solium three to four months, and that of 

 T. cchinococcns longer still. 



With one single exception (Archigetes) the 

 pisiformis in an evagi- larvae do not become sexually mature in the organ 



FIG. 203 Cysticercus 



siformis in an evagi- 



nated condition, with 



neck, fore-body and where they have developed ; they must enter the 

 terminal host, a matter that is usually purely 

 passive, the carriers of the larvae or infected parts 

 of them being usually devoured by other animals. In this manner, for 

 instance, the larvre (Cysticercus fasciolar is) found in mice and rats reach 



