CONTRIBUTIONS TO MARINE BIONOMICS. 229 
through the antennal tube, and carrying upwards the water which had 
previously bathed the gills. This current was caused, according to 
Gosse, by the “vigorous vibration of the foot-jaws.” The crab observed 
by Gosse was sitting on the top of the sand—not beneath it. 
If some sea-water be coloured by the addition of a little Chinese ink, 
or finely powdered carmine (the former is the better material), and if a 
few drops of the coloured water be added to the water in the neighbour- 
hood of the antennal tube of a buried crab, it will invariably be found 
that the current which sets through the antennal tube is from above 
downwards, and not vice versa. The same current may often, and indeed 
generally, be shewn to exist, even when the crab is not imbedded in the 
sand. 
It will then be noticed that the coloured water is sucked between 
the hairs of the antennal tube, and passes downwards and backwards 
to the prostomial chamber. Here, in front of the labium, the current 
divides into two streams, one right and one left, which pass outwards 
and backwards into the right and left branchial chambers respectively. 
Finally, the coloured stream emerges from the branchial chamber 
beneath the edge of the branchiostegite, not at any one point, situated 
either anteriorly or posteriorly, but along its whole extent, and espe- 
cially between the bases of the legs. 
The direction of this current through the branchial chamber is the 
reverse of that which has hitherto been recognised in all other Decapod 
Crustacea. In these (¢.g., Maia, Cancer, Carcinus, Astacus) the current 
which bathes the gills is known to enter this chamber beneath the 
branchiostegite, and to emerge in front by the lateral aperture at the 
side of the mouth. The normal peribranchial current in Decapod 
Crustacea is from behind forwards; I shall, therefore, term the 
current of the buried Corystes a “reversed current,” and shall speak 
of the whole phenomenon as a “reversal” of the normal current. 
Although Corystes cassivelaunus constantly exhibits this reversed 
current when imbedded in the sand, yet it is occasionally possible 
to observe the normal current in the same specimen when the animal 
is not buried. The coloured water is then rejected when added near the 
antennal tube; but if deposited near the bases of the legs, is sucked 
inwards, and eventually emerges from the branchial cavity into the 
prostomial chamber, and thence passes either directly to the exterior or 
forwards by way of the antennal tube. When the normal current is at 
work it frequently happens that the exopoditic palps of the maxillipeds 
begin to vibrate. The action of these palps still further intensifies the 
force of the exhalent currents, and at the same time disperses the 
streams of water laterally, ze, the water, instead of passing to the 
exterior anteriorly in an even stream, is partially diverted to the sides of 
