STRUCTURE AND DEVELOPMENT OF ECHINOCOCCUS 



349 



The development in cattle often remains stationary at the bladder 

 stage, and they are then called "acephalocysts," or Echinococcus cysticus 

 sterilis. According to Lichtenheld, sterile cysts occur in 80 per cent, 

 of cases in cattle, in 20 per cent, in pigs, and in 7*5 per cent, in sheep. 

 In other cases large numbers of small, hollow BROOD CAPSULES are 

 formed in the germ layer, but are not arranged in any particular order. 

 The order of the layers is just the reverse in them to what it is in the 

 parent cyst, that is to say, they have inside a thin non-laminated cuticle 

 and the parenchymatous layer on their external surface. These, 

 theoretically at least, may be regarded as invaginations of the bladder 

 wall giving rise to a cavity with the cuticle internal and the 

 parenchymatous layer external. If we suppose the orifice to close, 

 we should then get an isolated 

 cavity with cuticle internal and 

 parenchymatous layer external, as 

 in the brood capsule (fig. 252). 



FlG. 252A. 



If we next suppose an evagination of the wall of the brood capsule to 

 occur at one point we should get a hollow process lined with cuticle ; 

 at the bottom of this we get the scolex and hooklets formed, and a 

 little higher up the tube the suckers (fig. 252, 4). If this hollow scolex 

 is now pictured as being invaginated we get a hollow scolex covered 

 with cuticle and lined by a parenchymatous layer projecting into the 

 cavity of the brood capsule. The two sides of this hollow scolex now 

 fuse and we get a solid scolex projecting into the cavity. Finally, if 

 we imagine once more the rostelium and suckers invaginated into the 

 posterior part of the scolex we get the condition as frequently found 

 in the brood capsules, i.e. f a scolex covered with cuticle projecting into 

 the cavity, with the rostelium and suckers invaginated into the posterior 

 portion of the scolex (fig. 252A, 7). 



