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, etc., Diesing, Systema Helminthum, ii. 1851. Revision, Id. SB. Akad. Wien, xlii. i860; von Drasche, Verh. z. b. Gesellsch. Wien, xxxii. 1882; xxxiii. 1883.

Hosts, etc., von Linstow, Compendium der Helminthologie, Hannover, 1878.

Free-living Nematoda, De Man, Monograph, Leiden, 1884 (cf. Tijdschr. Ned. Dierk. Vereen, v. 1880); Nordsee-Nematoden, Id. Leipzig, 1886; Orley, Monographic der Anguilluliden, Buda-Pesth, 1880; Butschli, Abhandl. Senck. Gesellsch. ix. 1873-75; Id. Nova Acta, xxxvi. 1873; Bastian, Ph. Tr. 155, 1866.

Plant-Parasites: Tylenchus Tritici = Anguillula scandens, Davaine, Recherches sur l'Anguillule du ble' nielli, Paris, 1857. T. Dipsaci, Kuhn, Z. W. Z. ix. 1858. T. Millefolii, Low, Verhandl. z. b. Gesellsch. Wien, xxiv. 1874. T. putrefaciens (of Onion), Chatin, Paris, Gauthiers-Villars, 1884; cf. C. R. 98. Cf. for summary, Braun, SB. Natf. Freunde, Berlin, 1875.

Haematozoa: Filaria sanguinis hominis (=F. Bancroft), etc, Manson, London, Lewis, 1883; Id. Tr. L. S. (2), ii. pt. 10, 1884; of Man, Lewis, Q.J. M. xix. 1879; of Dog, Megnin, Journal de PAnat. et Physiol, xix. 1883, and Lewis, Q. J.M. xv. 1875.

Lung-parasites of Cattle and Sheep, T. S. Cobbold, Journal Royal Agricultural Soc. England, (2) xxii. 1886; Nematodes of Sheep's lung, Koch, Oesterreich. Monats-schr. Thierheilkunde, 1883.

Animal Parasites. Angiostomum, von Linstow, A. N. 51, 1, 1885. Rhabdonema (= Anguiltula stercoralis and A. intestinalis), Id. ibid. pp. 11-12; cf. Grassi, Anchilostomi ed Anguillule, Naples, 1882 (Gazetta degli Ospitali, 1882), and Seifert, SB. Phys. Med. Gesellsch. Wurzburg, 1883. Oxyuridae of Insecta, Galeb, A. Z. Expt. vii. 1878. Anchylostoma (Dochmius) duodenalis, Schulthess, Z. W. Z. xxxvii. 1882. Syngamus trachealis (Gapes disease), Ehlers, A. N. H. (4), ix. 1872; Megnin, Bull. Soc. Zool. France, 1880, or Id. 'On the Gapes Disease,' London, 1883. Id. Sclerostoma Boularti from trachea of Cassowary, Journal de l'Anat. et Physiol. xx. 1884. Filaria rhytipleurites of Cockroach and Rat, Galeb, A. N. H. (5), ii. 1875. Lchthyonema, von Linstow, A. N. 40 1, 1874. Mermis, Meissner, Z. W. Z. xiv. 1854. Sphaerularia, Schneider, Zool. Beitrage, i. 1883-85, and Leuckart, Z. A. viii. 1885. Simondsia, Cobbold, Tr. L. S. (2), ii. pt. 8, 1883.

Muscles, Rohde, 'Beitrage, etc.,' Schneider's Zool. Beitrage, i. 1883-85.

Nervous system, Schneider, op. cit.; Joseph, Z. A. vii. 1884; Butschli, A. M. A. x. 1874; origin of, Id. M. J. x. 1885.

Sexual organs: $ and spermatogenesis in Ascaris megalocephala, E. van Bene-den and Julin, Bull. Acad. Roy. Belg. (3), vii. 1884; cp. Hallez, C. R. 98, 1884; Nussbaum, A. M. A. xxiii. 1884; Schneider, Das Ei und seine Befruchtung, Breslau, 1883; $ with forms of spermatozoa in same, E. van Beneden, Archives de Biologie, iv. 1883. Maturation of ovum and impregnation, Id. op. cit.; cf. Nussbaum and Schneider (supra), and the latter in his Zool. Beitrage, i. 1883-85, p. 131; germinal vesicle and polar globules, Carnoy, 'La Cellule,' ii. (1), 1886.

Male Trichodes (= Trichosomum) in utero, von Linstow, A. N. 40, 1, 1874; Butschli, A. N. 38, 1, 1872.

Encystment of Trichina, Chatin, A. Sc. N. (6), xi. 1881.

Life-histories: see general works cited above, and Balfour, Comp. Embryology, i. pp. 309-13.

Gordiidae, Vejdovsky, Z. W. Z. xliii. 1886; Villot, A. Z. Expt. iii. 1874; Id. A. Sc. N. (6), xi. 1881. Host of, von Linstow, Z. A. vi. 1883; Villot, Z. A. vii. 1884. Affinities: see Vejdovsky.