

ACANTHOCEPHALA ANATOMY 



177 



and which, by means of the contractions of their muscular coat, 

 force the fluid into the lacunae when the proboscis is everted, 

 and thus aid in its protrusion. 



The parasitic habits of Echinorhynclius. have had a deeper 

 influence on the structure of the body than is the case with the 

 Nematoda. All traces of an alimentary canal have disappeared, 

 and the animals live entirely by the imbibition through the skin 

 of the already elaborated fluids of their hosts. The power of 

 absorbing fluids is shown by the fact that they swell up and 

 become tense when placed in fresh water. 



Until recently no definite excretory organs had been recognised, 

 and the function of excreting the nitrogenous matter was by 

 some assigned to the lemnisci. * 



In 1893 Kaiser 1 described 

 in 6r. gig as two organs 

 which he called nephridia, 

 placed dorsally to the ducts 

 of the male and female 

 reproductive organs. Each 

 nephridium, which somewhat 

 resembles a cauliflower, con- 

 sists of a stalk or duct, 

 opening at one end into 

 the reproductive ducts, and 

 at the other branching 

 and breaking up into a 

 number of secondary and 

 tertiary twigs. The end of each twig is closed by a mem- 

 brane pierced with a number of most minute pores, by 

 means of which it communicates with the body -cavity ; on 

 the inner side the membrane bears a number of long cilia, 

 which keep up an active flickering. The presence of these cilia 

 is interesting, as elsewhere they are unknown throughout the 

 Nemathelminthes. 



The nervous system consists of a central ganglion situated in 

 the proboscis sheath ; it is oval and flattened in shape. The 

 ganglion gives off nerves to the proboscis, and two main trunks 

 which pierce the proboscis-sheath and run backward surrounded 

 by a cluster of muscle - fibres, the whole being termed the 



1 Bibl. Zool. Bd. ii. Heft 7. 1893. 

 VOL. II N 



Fig. 95. A, A longitudinal section through 

 the terminal twigs of the nephridium of 

 Gigantorhynchus gigas. (From J. E. Kaiser.) 

 Highly magnified, a, Nucleus. B, A ter- 

 minal twig more highly magnified ; b, the 

 porous membrane. 



