ENTOZOA. 61 



human body. They resemble the Nematoid Entozoa in outward 

 form, and in the distinction of the sexes, but in their digestive system 

 they still manifest the sterelminthic type. 



The species of this order constitute but one genus, Echinorhynchus, 

 characterised by a more or less elongated, round, subelastic body, the 

 head having a retractile proboscis armed with recurved spines. The 

 Echinorhynchi abound in the lower animals, and are, some cylindrical, 

 and others sacciform. The largest known species {EchinorJiynchus 

 gigas) infests the intestines of the hog. As regards the tegumentary and 

 muscular system, it resembles the Nematoid worms, as well as in its 

 dioeceous generation; but its digestive system is very different, and some- 

 what obscurely developed. The mouth is a minute pore, situated on the 

 extremity of the uncinated proboscis : it leads to two long cylindrical 

 canals, which adhere to the muscular tunic, and are continued to the 

 posterior extremity of the body, where they terminate in blind ends ; 

 and two shorter cylindrical coeca are continued backwards from near 

 the mouth, and are freely suspended in the anterior part of the 

 generative cavity : they are called lemnisci. The male organs 

 consist of two fusiform testes, two vasa deferentia, which unite 

 together to terminate in a single vesicula seminalis, and a long 

 intromittent organ provided with a bursa occupying the posterior 

 extremity of the body, and having a special muscular apparatus for 

 the retraction and extrusion of the contained organ. The male echi- 

 norhyncus is generally half the size of the female. The generative 

 organs in this sex consist of two ovaries and one oviduct. The ovaries 

 are long and wide cylindrical canals, which of themselves occupy 

 almost the whole cavity of the body, extending from the proboscis to 

 the tail, and the common slender oviduct terminates at that extremity 

 by a very minute pore. The best details of the anatomy of this order 

 are given by Dr. Westrum* and by Dr. Cloquet, in his prize Essay on 

 the Anatomy of the Intestinal Worms, f 



LECTURE VL 



ENTOZOA. 



The four orders of the class Entozoa which have already been 

 described, are less natural than the order Nematoidea, which will 



* De Helminthlbus Acanthocephalis, fol. 1821, 

 t Anatomie des Vers Intestinaux. 4to. 1824. 



