EECENT WOEKS OIV THE ENTOZOA. 345 



and other Nematoids so well studied by Kolliker, lias, thanks to the 

 researches of Nelson, become famous in the history of embryology. 

 Trichina spiralis, equally with the cysticercoid state of Tcenia solium, 

 is a common parasite of the pig. Lastly, it is interesting to note 

 that the blood-worm of man has been detected by Dr. Cobbold within 

 the portal vein of Cercopitliecus fuliginosus. Most of the remaining 

 Helminths in the above list would seem, so far as at present known, 

 peculiar to the human species. 



And now as to the parts of the body which the human Entozoa 

 infest, a few words may be said. The Trematoda afiect various 

 •viscera, both solid and hollow, and two species {Bilharzia licematobia 

 and Hexatliyridium venarum) have even been found in the blood. 

 The Cestoidea, in their strobiloid stage, occur only within the ali- 

 mentary canal, to which some of the ancients supposed all human 

 parasites restricted. This opinion is clearly stated in a rather obscure 

 passage in the works of the now \\ti\Q vQSkdi ^oet Apopliantiacus, which 

 may be thus rendered : — 



Tell me, where is Taenia bred ; 



In the guts, or in the head ? 



In the former, truly. 



Kindly Providence confines 



To the human intestines 



Parasites unruly. 



But the scolices of the same worms, especially of T<^nia ecliino- 

 coccus, " may be found in any part and in any of the tissues, in- 

 cluding the bones themselves." Among Nematoids, the guinea-worm 

 takes up its abode within the cellular tissue, coming closer to the 

 surface when mature. Another species of JDracunculus {D. loa) 

 occurs commonly beneath the conjunctiva of negroes. To the same 

 category, of eye-parasites, belong also Filaria lentis and one or two 

 forms of Trematoda, besides the Cysticercus cellulosa. .Trichina 

 spiralis, in its most familiar phase, is essentially a parasite of the 

 muscular system. Strongylus hronchialis and Filaria trachealis select 

 the respiratory organs. Most of the other human Nematoids inhabit 

 the digestive canal. 



"With regard to his Cestoid parasites, the position man occupies 

 is altogether peculiar. He is the only animal species in which the 

 scolex and strobiloid condition of the same tape- worm have both been 

 observed. This is true of two species, at least, Tcenia solium, and T. 

 medio-canellata. The strobiloid stages of these tape-worms are un- 

 questionably derived from without. But how have their scolices 



