32 HISTORY OF CRUSTACEA. Chap. Y. 



I have also observed the same elevation of the cara- 

 pace in some species of the allied genera Sesarma and 

 Cyclograjpsus, which dig deep holes in marshy ground, 

 and often run about upon the wet mud, or sit, as if 

 keeping watch, before their burrows. One must, how- 

 ever, wait for a long time with these animals, when 

 taken out of the water, before they open their branchial 

 cavity to the air, for they possess a wonderful arrange- 

 ment, by means of which they can continue to breathe 

 water for some time when out of the water. The 

 orifices for the egress of the water which has served for 

 respiration, are situated in these, as in most Crabs, in 

 the anterior angles of the buccal frame (" cadre buccal," 

 M,-Edw.), whilst the entrant fissures of the branchial 

 cavity extend from its hinder angles above the first 

 pair of feet. Now that portion of the carapace which 

 extends at the sides of the mouth between the two 

 orifices (" regions pterygostomiennes "), appears in our 

 animals to be divided into small square compartments. 

 Milne-Edwards has already pointed this out as a par- 

 ticularly remarkable peculiarity. This appearance is 

 caused partly by small wart-like elevations, and partly 

 and especially by curious geniculated hairs, which to a 

 certain extent constitute a fine net or hair-sieve extended 

 immediately over the surface of the carapace. Thus 

 when a wave of water escapes from the branchial 

 cavity, it immediately becomes diffused in this network 

 of hairs and then again conveyed back to the branchial 

 cavity by vigorous movements of the appendage of the 



