INSECTS AS PARASITES 



189 



fortunate star-fish may also present a number of rounded swellings 

 in which are lodged parasitic snails of another species (Stilaster 

 Linckue) that have undergone much further modification, being 

 practically endoparasites in which the proboscis has become very 

 long, while the rest of the body is much smaller in proportion, 

 and the shell has disappeared. Communication with the exterior 

 is still kept up, however, by means of a small hole, in the interests 

 of breathing and the getting rid of waste products. From this 

 case we pass on to degenerate worm-like snails, which are true 

 internal parasites, and have lost most of the typical organs of the 

 group to which they be- 

 long, though the study 

 of their life- histories 

 renders no doubt pos- D.G. 

 sible as to their classifi- 

 catory position. Their 

 bodies hang freely into 

 the interiors of their 

 hosts, one end being 



fixed tO the inner Side Fig. 1134. -Parasitic Cap-Shell (Thyca ectoconcha} attached to the 



of the hnrlv Wall nf tVlP Skinof a Star-Fish (Linckia multiforis}; diagrammatic section. D.G., 



Digestive gland; F.G., foot-ganglion; S., S., suctorial disc; ot., otocyst. 



same. A degenerate 



of the kind (Entocolax Ludwigii} lives within a species of sea- 

 cucumber (Myriotrochus Rinkii), and one still more strongly 

 modified (Entoconcka mirabilis) within another creature of the 

 same sort (Syapta digit at d). 



The parasitic habit of the larvae of Freshwater Mussels has 

 been dealt with elsewhere (see vol. iii, p. 406). 



Cut 



ot 

 F.G. 



Foot 



INSECTS (INSECTA) AS PARASITES 



Innumerable insects have adopted the parasitic habit, either 

 for the whole of their lives or for some particular stage of exist- 

 ence. It will only be possible to give a limited number of 

 examples in illustration of the more interesting kinds of adap- 

 tation. 



BUGS (HEMIPTERA) AS PARASITES. The fact that the insects 

 of this order possess piercing and sucking mouth-parts naturally 

 suggests that some of them attack other animals, which is indeed 

 the case, though the majority would appear to devote themselves 



