230 CONTRIBUTIONS TO MARINE BIONOMICS. 
the crab’s body, and is scattered outwards and laterally by the vigorous 
lashings of the exopoditic palps. 
Gosse’s observations on the respiratory currents of Corystes cassive- 
launus are thus seen to be incomplete rather than inaccurate. A 
current may be directed outwards through the antennal tube, and the 
effete water from the branchial chamber may be carried away by that 
channel; but such a direction of the current in Corystes cassivelaunus is 
not constant, as Gosse believed, or even usual. Moreover, when the 
crab is imbedded in sand, the current is always reversed, except for 
a few seconds now and then, when the crab desires to eject distasteful 
particles which have entered the prostomial chamber with the respira- 
tory current. Under such circumstances the reversed inhalent current 
through the antennal tube is temporarily replaced by a forcible exhalent 
current. But as soon as the desired ejection has been effected, the 
reversed current is again set up. This voluntary inhibition of the 
reversed current can be easily demonstrated by the addition of carmine 
to the water setting through the antenne. Oddly enough, a weak 
solution of Chinese ink is less distasteful to Corystes than a mixture 
of powdered carmine and sea-water. 
(c) Cause of the Currents. The direction of the respiratory currents 
is exclusively due to the movements of the scaphognathite, the valve- 
like and highly muscular appendage of the second maxilla, which 
is known to produce the regular respiratory currents of other Decapoda. 
H. Milne-Edwards first demonstrated the important rdéle played by the 
scaphognathite in Decapod Crustacea; and he maintained that the 
direction of the respiratory current was absolutely constant, 2.2, from 
behind forwards in all Decapods (1839, p. 136). De Haan (1850, 
p. 117) has indeed suggested that the current to the branchize passes 
from before backwards; but his remarks on this subject are obviously 
the result of mere inference, and are not determined by actual experi- 
ment. He states, for example, that in Portunus the inhalent current 
sets inwards not only through the aperture between the base of the 
cheliped and the edge of the branchiostegite, but also through the 
anterior aperture at the side of the mouth, Experiments on Portunus 
have shewn me that this is quite devoid of foundation; the water 
certainly enters—in part—through the former of these apertures, but 
the aperture at the side of the mouth is invariably exhalent in function. 
In the case of Corystes I observed the action of the scaphognathite by 
removing the three maxillipeds and the edge of the pterygostomial 
fold of a living specimen. The scaphognathite was completely ex- 
posed by this preparation, and its movements were readily followed. 
When the normal current—from behind forwards—was at work, the 
propulsion of the water could be seen to be effected by a sharp, prompt 
