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 (e.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, i.e., the water, instead of passing to the 

 exterior anteriorly in an even stream, is partially diverted to the sides of 



