60 



NATURAL HISTORY OF ARTHROPODS. 



consistence the abdomen of the true hermit crabs, and, for protection, ffi/poconcha 

 takes a half of a bivalve shell, and inserting the angle of its abdomen in the depression 

 beneath the hinge, holds the shell in position by the fourth and fifth pairs of thoracic 

 feet. A similar habit has been noticed in the Chinese genus, Conchoecet.es. In some 

 of the sub-genera of Dromia the crab carries in a similar manner a sponge, polyp, or 

 compound ascidian. 



FIG. 73. Dromia covered with a sponge. 



The remaining groups of Brachyura all have the female genital openings on the 

 ventral surface of the body, between the bases of the feet, while in the zoeas a dorsal 

 spine is almost universally present. 



The MAIOIDEA or Oxyrhyncha, which in the older works were regarded 

 as forming the highest of the Decapoda, and, indeed, of the whole Crustacea, are in 

 reality the next in order ; for although in some respects they have a high grade of 

 structure, they, nevertheless, retain many embryonic features even in the adult stage, 

 the young Cancer, for instance, at a certain portion of its development being strongly 

 maioidean in appearance. The antennulse are folded in longitudinal pits in the front of 

 the carapax. The external maxillipeds are broad, the fourth joint being borne on the 

 inner angle, or the summit of the third, while the carapax is usually elongate and tri- 

 angular, being narrowed in front. The Maioidea are divided into several families and 

 over a hundred genera, the distinctions, however, being of too technical a character to 

 suit a work like the present, the systematic student being referred to the paper by 

 Mr. E. J. Miers in the Journal of the Linnean Society for 1879. 



