STRUCTURE OF THE HEAD. 751 



manner, which is probably not without influence on the width of the 

 vascular spaces. 



The great histological differences between the ribbon-shaped body 

 of this worm and the subsequent chain, furnish sufficient evidence 

 that the former is not directly metamorphosed into the latter, but, 

 like the body of Cysticercus fasciolaris, is lost in the transition to the 

 final state, and is replaced by a new formation. The same is probably 

 true of related forms with longer larval bodies. In all probability the 

 head and the immediately adjacent portion persist to form the origin 

 of the jointed body. 



The constitution of the head is but little known. Cobbold gives 

 no report on the subject ; his specimens apparently had their heads 

 wholly retracted, and in mine the latter is only half protruded. So 

 much, however, I may affirm, that the head has an 

 unusually compact appearance. It appears in my 

 specimen as an almost hemispherical protrusion, 

 which is traversed on either side by a superficial 

 furrow. Both furrows can be traced to the hole 

 occupying the apex of the protrusion, and are there- 

 fore not free throughout their whole length. There 

 are no distinct lips unless one can so regard the 

 ridge-like protruding boundaries of the furrow. The tig. ioi. — Head 



state of affairs further forward I was forced to leave »? , SothrhcepMus 



lic/uloides. (x 5.) 



undecided. 



The life-history also of this parasite is still unknown. "We are 

 left to mere conjectures that the host of the adult worm is a car- 

 nivorous animal which comes into close association with man. It 

 may be likewise presumed that man is not the only host of this form. 

 It seems likely that the dog or cat, or even the pig,^ is in some way 

 implicated in the history of this parasite. That it occurs also in cold- 

 blooded animals is, considering the great difference in the conditions 

 of life, as probable as the supposition that the host of the adult worm 

 is likewise cold-blooded. 



^ The pig is not, indeed, a domestic animal throughout Japan, but, according to my 

 Japanese pupils, is kept in the island Kiushiu, where the host above referred to was 

 probably infected, and in the whole province of Satsuma, to which the island belongs. 



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