president’s address. 
125 
Corystes cassiveluunus is a Crab which is common in the deeper 
water all round the British Isles, and is characterised by the great 
length of its second antennae. These antennae can be apposed so 
as to form an elongated tube by the interlocking of two rows of 
hairs placed respectively on the dorsal and ventral borders of each 
antenna with the corresponding hairs of the opposite antenna. 
Mr. Garstang, while confirming the earlier observations of Kobertson 
and Gosse that the tube formed by the antennae serves as a passage 
for the water used in respiration, adds important information with 
regard to the mode of action of this tube. Corystes has the habit 
of burrowing in sand, which it does by sitting upright on the sur- 
face and rapidly pulling itself backwards by means of its walking 
legs. It thus descends into a position where, it is secure from the 
observation of predatory fishes, leaving only the tip of its antennal 
tube projecting beyond the surface of the sand. In this condition 
it remains during the day, but probably comes out at night to take 
food. 
While in most of the Decapod Crustacea the water employed in 
respiration usually enters the gill-chamber beneath the branchio- 
stegite and leaves it by an aperture placed at the side of the mouth, 
the current is constantly maintained in the opposite direction by 
a Corystes which is lying in the sand ; the water thus entering the 
antennal tube, the hairs of which serve to prevent sand from coming 
in as well. The direction of the current is easily demonstrated by 
experiments with coloured water. Under certain circumstances, 
the current in Corystes has the same direction as in most other 
Decapods.* 
This is, however, by no means the only case in which Mr. Garstang 
has been able to show that some of the most obvious external 
characters — for which no adequate explanation had previously been 
suggested — are similarly connected with the respiratory phenomena.-) 
* It has been shown by G. Bolm (Ann. Mag. Nat. Hist. (7) vol. i., 1898, 
pp. 17, 20) that the reversal of the direction of the respiratory current is 
a common phenomenon among Crabs. 
t “The Function of Autero-lateral Denticulations of the Carapace in 
Sand-burrowing Crabs,” Journ. Mar. Biol. Ass. vol. iv. (N.S.), 1895—97, 
p. 396. 
