CONTAGIOUS DISEASES OF DOMESTICATED ANIMALS. 109 



iuch) than the diameter of the middle of the body. Vulva springing 

 from the base of an inclined neck, which is 1.5'"™ to 3""" (.059 — .118 inch) 

 long. Ova innumerable, smooth, elliptical, .085""" to .09""" (.0033 — .0035 

 inch) long, and .05"'"" (.002 inch) broad, each pole closed by a hood-like, 

 hemispherical valve, which becomes entirely detached at the time of 

 hatchiug. Embryos eel-like, developed in the body of the female, which 

 sets them at liberty only by its death and the destruction of its body ; 

 at birth they measure .28"^"^ (.011 inch). 



Habitat of the adults. — Trachea of pheasants. 



We shall now studj^ in detail the various parts of the body in the fol- 

 lowing order : 



1. The general envelope of the body, consisting of the cuticle and the 

 muscular layer lining it ; 2, the digestive tube with its accessory parts; 

 3, the nervous system ; 4, the system of excretory vessels ; 5, the male 

 aud female genital ajiparatus as it exists in the most highly developed 

 adults. 



Body envelope. — The cuticle (Plate I, Fig. 5, «, a) is very thin, about 

 .05™"' (.002 inch) thick, diaphanous, in appearance homogeneous, for we 

 have been unable to distinguish several layers, as has been done with 

 the larger nematodes. In young subjects it bears fine transverse strife, 

 but in old and united pairs of which the female is bearing eggs, and es- 

 pecially when these eggs contain well-developed embryos, the stride of the 

 trunk are completely effaced, but persist on the neck, where they can 

 be best seen in the female, in which they are .087™™ (.0031 inch) apart 

 each fourth or fifth being deeper than the rest. Around the mouth the 

 cuticle expands like a collar or gamopetalous corolla, with four equal 

 rounded divisions forming four lips. At the same time it furnishes a 

 broad margin to the thick and scalloped border of the buccal armature. 

 In the male the cuticle goes to form the caudal, bell-shaped bursa, 

 which is cleft posteriorly and longer anteriorly, the latter aspect being 

 probably the true dorsal aspect of the worm. This bursa is supported 

 by six simple rays on each side. It caps the hemispherically projecting 

 vulva of the female and is united to it so intimately that even after the 

 death of the worms and their maceration in water it becomes torn be- 

 fore it can be separated from the vulva. 



The muscular layer which lines the internal surface of the cuticle 

 forms four longitudinal bands, as among the other nematoid m orms, two 

 dorsal and two ventral, separated from each other by four linear inter- 

 vals. These muscular tracts are very delicate and permit the internal 

 organs to be seen through them. Only the superficial layer is distin- 

 guishable. It consists of longitudinal fusiform fibers (Plate I, Fig. 5, b) 

 aud is lined with i)arenchymatous cells, which may be regarded as a 

 deeper muscular layer. 



Digestive apparat us.— In the digestis'e tract three regions may be dis- 

 tinguished — the mouth, tlie a'sopliagus, and the intestine. 



The mouth (Plate I, Fig. 4, A, B) opens on the anterior extremity of 



