^99. 



THE HELMINTHES. 



101 



ORDER III. TREMATODES. 



The body is parenchymatous, and usually flattened. The intestinal canal, 

 which is often branching, has a mouth, but nearly always is without an 

 anus. The genital organs of both sexes are combined in the same indi- 

 vidual. Copulatory organs are present. 



Genera : Gyrodactylus, Axi7ie, Octobothrium, Diplozoon, PoJystomum, 

 Aspidocotylus, Aspidogaster, Tristomum, Monostomjtm, Holostomum, 

 Gasterostomum^ Pentastomum.* 



ORDER IV. ACANTHOCEPHALI. 



The sack-like bodj^ is flattened, transversely striated, and swollen cylin- 

 drically by the absorption of water. Digestive organs are wanting. The 

 genital organs are situated in separate individuals. Copulatory organs 

 are present. 



Genus : Echinorhynchus. , 



ORDER V. GORDIACEL 



The body is filiform and cylindrical. The digestive organs are without 

 an anus. The genital organs are situated upon separate individuals. 

 Copulatory organs are sometimes present. 



Genera : Gordius, Mermis. 



ORDER VI. NEMATODES. 



The body is sack-like and cylindrical. The digestive canal has a 

 mouth and an anus, and passes in a straight line through the cavity of the 

 body. The genital organs are situated upon separate individuals. Copu- 

 latory organs are present. • 



* In this connection, and especially in reference 

 to the remarks made by the author under § 99, it 

 may be well to notice that Fan Beneden does not 

 regard the Linguatulae as true Helminthes, but 

 that they belong rather to the division of articulated 

 animals, — coming nearest to the Lerneae. His 

 reasons are the following : 



" These anhnals, on their extrication from the 

 egg, are provided with two pairs of articulated feet 

 terminated by hooks. 



" The nervous system differs from that of the 

 Lerneae only in having two cords which form the 

 ganglionic chain, separated throughout their whole 

 length, whilst in the Lerneae they are separated 

 for only half their length. 



" In both cases the males are comparatively 

 very small. The ovisacs of the females are equally 

 bulky ; but in the Lerneae which live in water 

 they project externally, whilst in the Linguatulae, 

 which always live in a different medium, they 

 remain in the interior. 



9# 



" Besides the ring of nerves, the sub-ocsophageal 

 ganglion, and the cords which represent the 

 ganglionic chain, the Linguatulae are provided 

 with different ganglia representing the gi-eat sym- 

 pathetic. I detected four perfectly distuict ganglia 

 spread over the sides of the lower surface of the 

 oesophagus in the new species from the Mandrill. 

 In another species M. Blanchard detected these 

 ganglia and stomato-gastric nerves; but he referred 

 them to the system of the nerves of relation or 

 those of animal life, judging, at least, from the 

 name which he has assigned to them. 



" Another point, which, however, had not escaped 

 the attention of naturalists, is that the muscles 

 exhibit in then- primitive fibres the transverse 

 lines which are not met with in the lower ani- 

 mals." 



See Bull, de I'Acad. Royale de Belgique, 1848, 

 XV. No. 3. See also Blanchard, Comp. Kend. 

 1850, XXXI. p. 629. — Ed. 



