ZOOLOGY. 587 



these again into three families, in accordance with the 

 classes, namely, those of the Protozoa or Mucus-animals, 

 through which they pass. 



Order 1. Infusorial Worms Parasites. 



3605. The White-blooded Worms or Entozoa are very 

 imperfect animals, a fact which proves that this circle 

 recommences quite inferiorly or from below. They live 

 for the most part in the interior of other animals, being 

 thus located in darkness and in places where they obtain 

 but little oxygen. Their blood therefore is not simply 

 colourless, but even its vessels are only imperfectly 

 developed. They respire without doubt through the 

 tegument. In many, a distinct or separate intestine 

 being wanting, it is the tegument also which digests ; in 

 others the intestine is simply a sac without an anus. The 

 sexual parts too are in many species of a doubtful cha- 

 racter, while meantime there are both androgynous 

 and dioecious individuals. In the latter the male parts 

 open invariably at the posterior extremity of the body, as 

 in Insects ; the female parts in front of its caudal end, as 

 in the Crustacea. Both are in other respects constructed 

 as in Insects, namely, there are two oviducts or seminal 

 ducts, which unite before reaching their external orifice. 

 They divide into three groups. 



In one of these the body is tolerably smooth, and the 

 pharynx commencing from a simple suctorial mouth elon- 

 gates into a ramified intestine without an anus ; they are 

 androgynous Saugic tinner. 



In others the body itself supplies the place of the sto- 

 mach; it is corrugated, and receives the food through 

 one or several orifices, without separating into a special 

 intestine. They have nearly all a claviform proboscis or 

 rostrum, with which they perforate substantial cavities for 

 themselves ; it would seem that they are both androgy- 

 nous and of separate sexes Hydatids and Tania. 



Others are separated into tegument and intestine like 

 the Mussels and Snails, but without having a distinct 

 vascular system, heart, and liver, though provided with a 

 nervous chord and separate sexual parts Ascarides. 



