108 



How Animals Changed 



body volume (Fig. 17). At Tortugas and on the North Carolina 

 coast a littoral aquatic crab has a body which is about twenty times 

 the volume of the gills, but in a land crab the body has sixty times 

 the volume of the gills (Pearse, 1929, 1929a) . A land hermit crab 

 will live several months after its gills have been removed (Borra- 

 daile, 1903; Pearse, 1929). An intertidal crab (Uca) may carry 

 water in its branchial chamber. "The fiddler crab is a true water- 



CRABS 

 AT BEAUFORT, NC 

 r^ll I .S DWINDLF TOWARD LAN D 







OCYPOOC 

 ALBCANS 



NUMBER 

 QFGILLi- 



:^.'-^w^v^.•'.^ 





Fig. 17. 



18 



18 

 18 

 16 



BOCYrQLL 

 RATIO 



671 

 631 

 491 

 461 



401 



361 



361 

 321 

 231 



breathing animal, but it can live in the air for several weeks with- 

 out changing the water in the gill-chambers" (Dembowski, 1926) . 

 Barnacles, on the other hand, though bound to the ocean forever by 

 their sessile mode of life and method of feeding, are terrestrial 

 rather than aquatic animals in their respiration (Monterosso, 1927) . 

 Verwey (1930) has classified littoral crabs according to their meth- 

 ods of respiration as follows: 



