* THE NEMATODE FAMILY GNATHOSTOMID^. 257 



The cuticle immediately behind the head-bulb always shows an 

 invagination foi'ming 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 for enabling the 

 worm to secure itself. 



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

 fine ti-ansverse striations, but otherwise smooth. The cervical 

 , papillse are usually situated a,t about one-fourth of the length of the 

 oesophagus from the anterior end. The excretoiy 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 more than 

 one-third of its length. 



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

 is provided with strong oblique muscles for this purpose. The 

 caudal alte ai'e rather well-developed, extending from a little in 

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

 are always eight pairs of caudal papillae, which vary very little 

 in arrangement in the different species. The papillae are of 

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

 and seventh pairs. The fourth and sixth paii-s are alv/ays 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 small, venti-al, circum-anal group very 

 much like tha,t seen in Spiroxi/s. All the lai'ge papillae in Tanqua 

 show an extremely chai'acteristic structure, having a very large, 

 swollen, basal portion and a finger-shaped termination. 



The spicules are equally characteristic. They are tubular, 

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

 appearance, owing to a covering of minute irregular granulations. 

 Only the extreme tip is smooth, and this is usually of smaller 

 calibre thari the shaft of the spicule, forming a little rounded or 

 conical projection. 



As regards the female organs, the vulva is situated in the 

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

 or shorter distance before opening into the uterus. The latter 

 may consist of two or four br-a,nches. When two branches 

 are present, they are opposed —i. e., one runs forw^ard and the 

 other backward. When four are present, three turn forward 

 and one backward. Various 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. 



