MODIFICATIONS OF STRUCTURE IN DECAPOD CRUSTACEA. 2l3 



figured iu this paper (Plate 12, fig. 1). But in Calappa the 

 buccal apparatus is completely covered by the chelipeds when 

 flexed, owing to the fact that these appendages are here pro- 

 vided with a pair of remarkable cockscomb-like crests on the 

 upper (anterior) margin of the hands (fig. 1, d). The margins 

 of these crests are serrated, but otherwise coincide with the 

 outline of the anterior region of the carapace during flexion 

 of the chelipeds. 



What is the meaning of this extraordinary opercular appa- 

 ratus furnished by the chelipeds in this genus, and why do the 

 chelipeds fit so nicely to the carapace during flexion ? 



I have found no satisfactory explanation from a study of 

 the literature dealing with the habits of these crabs. Risso 

 (1816, p. 18) states that crabs of this species " inhabit holes in 

 steep rocks 20 to 30 metres deep. When they are obliged to 

 abandon their usual retreats they withdraw their feet under 

 the carapace, draw their chelipeds together, and let themselves 

 fall like balls to the bottom of the water." He implies, in 

 fact, that the arrangement is an adaptation for defence, 

 similar to the ball-forming habits of the common wood-louse 

 (Ouiscus), or of its marine relative Armadillo. 



But it is now known that crabs of this genus do not usually 

 live upon rocky, but upon sandy shores, and that they possess 

 markedly fossorial habits (Macgillivray, 1852, p. 102 ; Hender- 

 son, 1893; Schmidtlein, 1879, pp. 24_, 25). I understand that 

 the sand-burrowing habits of this particular species have been 

 frequently observed in the tanks of the Naples aquarium. 



The only other suggestion which I have met with as to the 

 function of the chelipeds is contained in Schmidtlein's inter- 

 esting observations on specimens in the Naples aquarium 

 (1. c, pp. 24, 25). Schmidtlein states that the chelipeds serve 

 '" zum Einwiihlen und zum Schutze.^' It would appear from 

 his observations that the crab, if placed in a tank containing a 

 number of hungry fishes, protects from their thievish attacks 

 any morsels of food which it may be engaged in devouring, by 

 hiding them beneath its tightly closing chelipeds. Neither 

 this use, however, nor the act of burrowing, provides any 



