342 THE ANIMAL PARASITES OF MAN 



system. The rostrum represents a finger-shaped hollow process of the 

 cutaneous layer ; but, according to Hamann, it originates from the entoderm 

 and passes through the skin secondarily. It is covered by a thin cuticle 

 and, as a rule, contains a large number of regularly-placed chitinous hooks 

 that adjoin a granular formation tissue. From the base of the rostrum 

 springs a tubular hollow muscle extending into the body cavity this is the 

 Receptaculum proboscidis from the base of which again bundles of longitudinal 

 muscles originate, which pass along its axis and that of the rostrum itself, 

 and are inserted at the inner surface of its anterior end (retractor proboscidis). 

 These muscles when they contract invaginate the proboscis and draw it into 

 the receptaculum ; when reversed they act again as protrusor proboscidis - 

 The whole of the anterior body, however, can be invaginated, and for this 

 purpose there is a muscle that originates from the body wall at a variable 

 distance back, and which is joined to the receptaculum (retractor receptaculi) ; 

 there is also a bell-shaped muscle which springs from the body wall 

 behind the lemnisci in rings, and passes forward to the spot of attach- 

 ment of the lemnisci. 



The nervous system consists of a cluster of ganglia situated at the 

 base of "the rostrum, from which three nerves pass towards the front and two 

 towards the back. No sensory organs are known. 



The excretory organs, according to Kaiser, lie at the upper border 

 of the ductus ejaculatorius in the male, and at the so-called bell in the 

 female. Here they represent the long-known villous tufts, placed on disc- 

 like cushions. In each of the cylindrical villi which terminate blindly 

 towards the body cavity there lies a cilium, which springs from the mem- 

 brane lining the villus, and which lies in a space cavity of the villus, 

 which ultimately proceeds as a little canal. There are three canals discharging 

 into the uterus that serve to conduct the excretory materials from the body 

 cavity ; special glandular cells corresponding to the terminal cells of the 

 platyhelminths, at the commencement of the system, are not present in 

 the acanthocephala. 



Sexual Organs. 



A. Male organs. The greatest part of the male genital apparatus is 

 contained in a muscular sheath the ligament which originates at the 

 posterior end of the receptaculum proboscidis, passes along longitudi- 

 nally through the body cavity, and is inserted at the posterior end of 

 the worm. The two oval testicles usually lie one behind the other ; their 

 vasa efferentia unite sooner or later into a vas deferens which passes 

 backwards, and finally terminates in the penis j the terminal portion of the 

 conducting apparatus is surrounded by six large glandular cells (prostatic 

 glands), the excretory ducts of which open into the vas deferens. The 

 penis itself is placed at the base of a bell-shaped invagination of the 

 posterior end, the bursa, which is everted during copulation. 



B. Female organs. There are only two ovaries present in the liga- 

 ment during the larval stage. During the course of growth they divide 

 into accumulations of cells (placentulae, loose or floating ovaries), which 

 finally cause the ligament to burst, and they thus attain the body cavity. 



