CONTRIBUTIONS TO MARINE BIONOMICS. 227 



nexion there would be a risk of the animals being occasionally buried 

 to a dangerous depth by the accumulation of sand above them. Mr. 

 W. Thompson's statement that the antennae in very small specimens are 

 much longer in proportion to the carapace than in the adult harmonizes 

 well with this hypothesis, as to ensure safety the young would have to 

 burrow to a greater depth compared with the adults than would be pro- 

 portionate to their size." Mr. Hunt was not aware of Gosse's view 

 when he framed the above theory ; but, subsequently, in a footnote 

 to his paper, he referred to Gosse's theory as identical with his own. 

 The two are, however, essentially distinct, if I correctly understand Mr. 

 Hunt's language. According to Gosse's view, the function of the 

 autennaB is to produce a tube subservient to respiration; according 

 to Mr. Hunt's, the function of the elongated antenna3 is essentially 

 sensory, viz., to enable the buried crab to determine the depth to which 

 it burrows. The " danger " to which Mr. Hunt refers is clearly not the 

 danger of suffocation, but the danger of dislodgment from the sand by 

 wave-currents. The arenicolous habits of Corystes are adduced by Mr. 

 Hunt to illustrate one of the various methods adopted by marine 

 animals for resisting wave currents — a view which, in the case of 

 Corystes, I am unable to accept, partly on account of the normally deep 

 water habitat of the crab, and partly on account of evidence given 

 below which tends to shew that the burrowing habits of Corystes are 

 adopted primarily for concealment. 



IV. New Observations and Experiments. 



(a) Burrowing Habits. A number of living Corystes cassivelaunus 

 were placed in a series of vessels containing sand of different degrees of 

 coarseness, and it was soon noticeable that these crabs readily burrow 

 in fine sand, but find great difficulty in penetrating very coarse sand or 

 gravel composed of small pebbles. Moreover, a crab that has obstinately 

 declined for several hours to burrow in coarse, gravelly sand, will imme- 

 diately bury itself, if placed in an aquarium of fine sand. In all cases 

 the process of burrowing is effected exclusively by means of the 

 thoracic legs. The crab sits upright on the surface of the sand ; the 

 elongated, talon-like claws of the four hindmost pairs of legs dig deeply 

 into the sand ; the body of the crab is thus forcibly pulled downwards 

 by the grip of the legs, and the displaced sand is forced upwards on the 

 ventral side of the body by the successive diggings and scoopings of the 

 legs ; the slender chelate arms of the first thoracic pair assist in the 

 process of excavation by thrusting outwards the sand which accumulates 

 round the buccal region of the descending crab. This action at the same 

 time, no doubt, loosens the sand in the immediate neighbourhood, and 



