ACANTHOCEPHALA. 315 



in both sexes. The most remarkable changes are. however, those undergone 



O f J O 



by the rudiment of the proboscis. 



In its interior there is formed a cavity, but the wall bounding the front 

 end of the cavity soon disappears. By the time that this has taken place 

 the body of the adult completely fills up the larval skin, to which it very 

 soon attaches itself. The hollow rudiment of the proboscis then becomes 

 everted, and forms a papilla at the end of the body, immediately ad- 

 joining the larval skin. This papilla, with the larval skin covering it, 

 constitutes the permanent proboscis. The original larval cuticle is either 

 now or at an earlier period thrown off and a fresh cuticle developed. The 

 hooks of the proboscis are formed from cells of the above papUla, which 

 grow through the larval skin as conical prominences, on the apex of which 

 a chitinous hook is modelled. The remainder of the larval skin forms the 

 skin of the adult, and at a later period develops in its deeper layer the 

 peculiar plexus of vessels so characteristic of the Acanthocephala. The 

 anterior oval appendages of the adult cutis, known as the lemnisci, are 

 outgrowths from the larval skin. 



The Echinorhyncus has with the completion of these changes practically 

 acquired its adult structure ; but in the female the ovaries undergo at this 

 period remarkable changes, in that they break up into a number of spherical 

 masses, which lie in the lumen of the generative ligaments, and also make 

 their way into the body cavity. 



The young Echinorhyncus requires to be transported to its permanent 

 host, which feeds on its larval host, before attaining to sexual maturity. 



BIBLIOGRAPHY. 



(392) B. Gr eef f . " Untersucliungen ii. d. Bau u. Entwicklung des Echin. miliarius." 

 A rchiv f. Naturgesch. 1864. 



(393) K. Leuckart. Die menschliclien Parasiten. Vol. n. p. 831 et seq. 1876. 



(394) An. Schneider. "Ueb. d. Bau d. Acauthocephalen." Archiv f. Anat. u. 

 Phys. 1868. 



(395) G. E. Wagener. Beitrage z. Entwicklungsgeschichte d. Eingeweidewiirmer. 

 Haarlem, 1865. 



