NEMATODA. 687 



The Gordiidae are regarded by recent writers as a group distinct from the 

 Nematoda, and Vejdovsky has proposed the name Nematomorpha for them. The 

 principal points of anatomy are the following : There is an ornamented cuticle, 

 pierced by pores containing processes of the subcuticula or hypodermis, which con- 

 sists of distinct cells in the anterior and posterior regions of the body, of a granular 

 nucleated matrix in the middle region. The muscle-cells are numerous, longitudinal, 

 and disposed in a single layer. The body-cavity is filled up to a certain period by 

 cells with distinct walls, which, during the evolution of the genital products, are 

 reduced to an epithelium lining the body-walls, covering the 'egg-' and 'sperm- 

 sacs,' and forming epithelioid mesenteries, which apparently constitute the walls of 

 the efferent genital ducts, &c. The nervous system is represented by a peri- 

 pharyngeal ring, a ventral cord composed of ganglion cells and nerve-fibres, and a 

 caudal ganglion. Papillae similar to those of Nematoda are the sole organs of 

 special sense, and are especially well developed on the ventral aspect of the tail of 

 the male. There is a digestive tract, with cellular walls ; the mouth appears to be 

 occluded in some species when they become free ; the anus is ventral and posterior. 

 A dorsal canal is regarded by Vejdovsky as excretory. The sexes are separate, the 

 tail of the male deeply cleft. The female genitalia consist of paired metamerically- 

 arranged ovaria ; of two laterally-placed ' egg-sacs,' in which the ova ripen ; of two 

 median ' egg-receptacula,' which narrow posteriorly into the oviducts ; of a large 

 receptaculum seminis dorsal to the digestive tract, with two ducts leading one into 

 each oviduct; of an atrium, which has glandular walls, opens posteriorly, and 

 receives the two oviducts. As to the male organs, the true testes are not known 

 (Vejdovsky) ; there are two vesiculae seminales, the homologues of the ' egg-sacs,' 

 supra ; and two vasa deferentia, continuous with the vesiculae and opening into the 

 dilated termination of the digestive tract, which is capable of partial evagination. 

 Villot's account differs from that of Vejdovsky, which has been followed here. 



There are two larval forms, both annulated. The first has a distinct head, 

 body, and tail. The head is in- and e-vaginable, armed at its base with three 

 circles of spines, and at its apex with three stylets, the whole forming a boring 

 apparatus. It is lost in the second larval form, which is more elongated than the 

 first. The first form of Gordius aquaticus is stated by von Linstow to inhabit a 

 Mollusc (Limnaeus), the second, the coelome of a carnivorous insect, e.g. Dytiscus, 

 Carabus, Mantis. Villot believes that fish form the proper host, the first form 

 occurring encysted in the mucous membrane of the intestine, the second free in the 

 tissues. The first has been recorded from the Frog, various fish, aquatic Insectan 

 larvae, and the Molluscan Planorbis and Limnaeus ; the second from the Frog, 

 various fish, a large number of adult Insecta, and some Spiders. The worm 

 becomes free after a time, lives in water, and after copulation the female lays its 

 eggs, which are cemented together by the secretion of the atrium. 



The characters of the nervous, digestive, and generative system are markedly 

 different from those typical of Nematoda. Vejdovsky has discussed the subject of 

 affinities in detail at the end of his paper cited below. 



Nematoidea, Beddard, Encyclopaedia Britannica (ed. ix.), xvii. 1884; Cobbold, 

 * Parasites,' London, 1879; Leuckart, 'Die Menschlichen Parasiten,' ii. 1876; 

 Schneider, 'Monographic der Nematoden,' Berlin, 1876. 



Genera, &a, Diesing, Systema Helminthum, ii. 1851. Revision, Id. SB. Akad. 

 Wien, xlii. 1860 ; von Drasche, Verh. z. b. Gesellsch. Wien, xxxii. 1882 ; xxxiii. 1883. 



