THE NEMATODE FAMILY GNATHOSTOMID^. 



257 



The cuticle immediately behind the head-bulb always shows an 

 invagination forming more or less of a "collar" round the neck. 

 In one species this invagination is so highly developed that the 

 worm can withdraw its entire head into a prepuce- like sheath of 

 cuticle. In species in which the collar is less highly developed, 

 portions of the host's tissues are not infrequently found caught 

 between it and the back of the head-bulb, so that the collar 

 appears to function as an accessory apparatus foi' enabling the 

 worm to secure itself. 



The cuticle of the body is thick and tougli, and is marked with 

 fine transverse striations, but otherwise smooth. The cervical 

 papillae are usually situated at about one-fourth of the length of the 

 Oisophagus jfrom the anterior end. The excretory pore is situated 

 at about the same level, or a little in front of it, on the ventral 

 side. The oesophagus is usually rather long, and the cervical 

 sacs relatively short, extending beside it to not moi'e tlian 

 one -third of its lengtli. 



The tail of the male is curled towards the ventral side, and 

 is provided with strong obli(|ue muscles for this purpose. The 

 caudal alte are rather well-developed, extending from a little in 

 front of the cloacal aperture to near the tip of tlie tail. There 

 a,re always eiglit pairs of caudal papilla*, which vary verjHittle 

 in arrangement in the different species. The papilla? are of 

 different sizes, the largest being always those of tlie third, fifth, 

 and seventh pairs. The foui'th and sixth paiis are always small, 

 and more ventral in position than the others. The cloaca, opens 

 at about the level of the fifth pair, and consequently the fourth 

 and sixth pairs form a snjall, venti'al, circum-anal group veiy 

 . much like tliat seen in Spiroxijs. All the large papillae in Tanqua 

 show an exti-emely characteristic structure, having a, very large, 

 swollen, basal portion and a. iinger-shaped termination. 



The spicules are equally ciiaracteristic. They are tubular, 

 cylindrical, and equal in length, and always present a rasp-like 

 a,p})eara,nce, owing to a, covering of minute irregular graiiidations. 

 Only the extreme ti|) is smooth, and this is usually of smaller 

 calil)re than the shaft of the si^icvde, forming a little rounded or 

 conical projection. 



As regards the female organs, the vulva is situa.ted in the 

 posterior half of the body. The vagina, runs forward for a longer 

 or shorter distance before o])ening into tlie uterus. The latter 

 may consist of two or four branches. AVhen two branches 

 are present, the}' a,re opposed — e., one runs forw^ard and the 

 other backward. When four are present, three turn forward 

 and one backward. Yarious swellings, functioning as recepta- 

 cula seminis or as egg-reservoirs, occur in the course of the 

 uterine tubes, but their position does not seem to be. constant. 

 In fact, the general shape of the uterus varies so greatly in 

 different specimens of the same species that the expansions of 

 the tubes appear to be of a temporary nature, and cannot be 

 made use of for systematic purposes. 



