ON PARASITES. 21 



The head, is usually somewhat square shaped, with four (rarely 

 six) lateral sucking discs placed symmetrically round the central 

 pore which represents the mouth. This central pore is the anterior 

 termination of the two lateral excavations in the parenchyma of the 

 body already alluded to. It is surrounded by a crown of hooklets 

 arranged in one or more rows, and of various sizes and shapes in the 

 different species. The design of these hooklets in combination with 

 the sucking discs is to anchor the animal firmly to the intestinal 

 mucous membrane, so as to enable it to nourish itself with the 

 alimentary juices of the animal which it infests. 



The hooklets probably fall off with age. 



The body is ribbcn-like, very long, white, marked by transverse 

 lines dividing it into joints. 



The mature joints or proglottides are bisexual, rupturing succes- 

 sively one after another. The joints nearest the head are always 

 younger than those more remote. Each new joint budding from the 

 posterior aspect of the head or scolex pushes backward the next in 

 age. The transverse striations are very obscure among the newer 

 joints. 



The genital pores are usually alternate, the males larger and more 

 anterior, the females smaller and more posterior. Male and female 

 organs perfect. The resting scolices according to species assume 

 the cystic forms, that with a hand-like appendage or that without 

 any appendage. 



The active scolices vary much with the strobila in length and 

 breadth. The embryos are armed with six hooklets, small and active. 



The eggs of those species assuming the cystic form are very small, 

 yellow. Those of the species assuming the two latter forms are 

 larger and lighter in colour. Habitat of mature animal, the intes- 

 tines. This family is very extensively distributed, being frequently 

 found in the human intestines and in mammalia generally. The rest- 

 ing scolices are found in the serous cavities and various tissues of the 

 smaller and more defenceless animals of whatever species which are 

 preyed upon by the larger and more formidable ones. They also 

 undoubtedly occur occasionally in the same animal whose intestines 

 are infested by the perfect tape worm. In the former case the six- 

 hooked embryos are cast into the outer world enveloped in their egg- 

 shells and subsequently swallowed. In the latter they escape from 

 the egg shells in the intestine of the animal subject to the mature 



