168 PRACTICAL PAEASITOLOGY 



passes them on into the uterus. The lumen of the hinder portion of 

 the bell is, however, of such a size that it will admit only bodies of a 

 certain shape, that, namely, of the enclosed ova. Bodies of other 

 sizes and shapes are returned through the ventral opening into the 

 body-cavity. It happens, however, that numerous enclosed ova are 

 returned to the body-cavity, with the unsuitable bodies, to be again 

 swallowed by the bell. This manoeuvre is continued until the stream 

 finally compels them to enter the hinder part of the bell, whence they 

 are passed on into the uterus. 



The entire sexual apparatus of the male will be seen to be enclosed 

 in a sheath, known as the " ligament " (ligamentum suspensorium) , 

 which takes its rise at the base of the proboscis sheath. A similar 

 ligament is present in the female, the posterior end of which enters 

 the bell and is attached to its base. In young worms it encloses 

 the ovaries, but when these break up and the placentulae escape into 

 the body-cavity, the ligament in the greater number of cases is 

 ruptured. 



Echinorhynchus gigas, the giant Acanthocephalide which inhabits 

 the intestine of swine, is very useful for demonstration purposes. Its 

 structural scheme differs from that of the smaller varieties in certain 

 definite points, the more important of these being : the structure of 

 the proboscis sheath and the bursa ; the presence of two retractor 

 muscles instead of one ; and of eight cement glands instead of six. 

 In the female, the ligament is composed of two tubes, in which the 

 placentulae remain and in which the eggs undergo development, not, 

 as in other species, in the body-cavity. This arrangement presupposes 

 a direct communication between the two ligament tubes (which also 

 communicate upon their inner surfaces) and the oviducts, which is 

 brought about in the following manner : the dorsal half of the 

 ligament passes into the mouth of the bell, while the ventral portion 

 is associated with the orifice from which the immature eggs are 

 thrown out, and projects backwards and beyond the orifice in the 

 form of a blind sac. The eggs of E. gigas diverge from the typical 

 Acanthocephaline shape (fig. 43). 



The ova of Acanthocephala are deposited within the body of the 

 host and reach the exterior in the faeces. Each contains a finished 

 embryo, of which, in spite of the transparency of the shell, scarcely 

 more than the hooks situated at the anterior edge is visible. The 

 shell may be burst open by means of pressure upon the cover-glass, 

 but this is very likely to injure the embryo. An infinitely better 

 method, and one first adopted by E. Leuckart, is the artificial infec- 

 tion of suitable intermediate hosts ; the larvae will then emerge spon- 

 taneously from the shell and will be found free in the intestine. In 

 favourable conditions it is sometimes possible to catch the larva, when 

 under the microscope, in the act of emerging. 



