306 MANUAL OF NATURAL HISTORY. 



come fixed as parasites, their limbs become rudimen- 

 tary, and they are not able to enjoy individual pro- 

 gression, although transported along with animals 

 upon whose juices they subsist. The females of the 

 Carcinoid genera nearly always carry their eggs in 

 long cylindrical tubes or ovarian sacs, which arise from 

 the last thoracic segment on each side of the body ; 

 the males are frequently very minute, and so unlike 

 those of the other sex, as to resemble totally distinct 

 species. The instruments by means of which the 

 Fish-Parasites retain their hold of the animals they 

 infest, are either sharp curved hooks or prehensile 

 sucking disks ; in the Helminthoid families the 

 mouth is very simple, but in the higher Carcinoid 

 forms rudimentary mandibles are seen, together 

 with antennae and often a single eye. One of the 

 most curious genera is the Diplozoon, well named 

 paradoxum, an animal which assumes the shape 

 of two united beings forming a kind of Siamese- 

 twins, the bond of communion being simply a nar- 

 row band. The bodies named Pedicellarice seen 

 scattered over the surface, and around the mouth 

 of various Echinoderms, have been considered by 

 Monro, Forbes, Oken, and Sharpey as organs of the 

 animals on which they are found. The discovery 

 by one of the authors of an animal resembling 

 those bodies on Voluta Vespertilio as a true para- 

 site on the skin, seems, however, to confirm the 

 views of Miiller, Lamarck, and Cuvier, in regarding 

 the Pedicellarice as independent parasitic organ- 

 isms. 



