126 
president’s address. 
Most of the Cyclometopa, a group which includes the Edible Crab 
( Cancer pagurus), the Shore-Crab ( Carcinus maenas ), and many 
others, are well-known to have the front margin of the carapace 
conspicuously denticulated, although the purpose of this arrange- 
ment had not previously been ascertained. Many of these Crabs 
have burrowing habits ; and actual observations on Bathynecies 
longipes at Plymouth showed that the animal comes to rest in such 
a position that the whole body is covered with sand, with the 
exception of the eyes and the anterior margin of the carapace. 
Against this are pressed the two great chelae, in such a way as to 
form two passages between themselves and the carapace. The 
entrance to these passages is guarded by the denticulations of the 
carapace, on which sand-grains were observed to rest. Coloured 
water was at once sucked down these passages to the gills. An 
important function of the denticulations of the carapace is thus 
shown to be the formation of a straining apparatus by which sand- 
particles are prevented from being introduced with the respiratory 
current. It is further shown that the various modifications of 
a certain carpal spine on the great chela, which has long engaged 
the attention of systematic Zoologists as an important specific 
character, are also correlated with the respiratory phenomena. The 
spine stops the flexion of the chela at the point which is most 
appropriate for enabling the appendage to take part in the formation 
of the respiratory passage; and “the variations in the form of the 
carpal spine in different species and genera are all functionally 
correlated with the different shapes and proportions of the carapace, 
and of the segments of the cheliped.” 
The results above indicated have been extended by Mr. Garstang 
by a study of preserved material of other species of Crabs;* and 
it can hardly be doubted that analogous phenomena are of common 
occurrence in this group. Thus in Albunea, which belongs to the 
Hippidea, a group widely distant from that to which Corystes 
belongs, a tube, presumably used in respiration, is formed by the 
* “ On some Modifications of Structure subservient to Respiration in 
Decapod Crustacea which burrow in Sand,” Quart. Jouru. Micr. Sci. vol. xl., 
1898, p. 211. 
