LAND CRUSTACEANS. 85 



The source of the moisture is a problem of some obscurity. It is of the very rarest 

 occurrence for a Coenobita to be found in the water except at the breeding period'. 

 Ortmann states quite distinctly that, out of many hundreds, he has never seen one in the 

 water. Nor have I myself succeeded any better in this respect. That they do visit the 

 sea, however, I am convinced by two facts. First, that Mr Stanley Gardiner had the 

 good fortune to find a specimen of G. perlatus in the water a few feet from the lagoon 

 beach in Minikoi. It is true that this was a female, but there were no eggs or young, 

 nor any traces of them, on her abdominal limbs. Secondly, that the body of a freshly 

 caught specimen is always moist, and in a great many cases (certainly the majority of 

 C. perlatus and C. rugosus) the shell actually contains a small quantity of salt water-. 



Another possible method of moistening the gills must not be overlooked. In some 

 experiments to test the effect of drying the gill chamber it soon became evident that 

 this was an impossibility. By the careful use of cotton-wool and blotting-paper, a great 

 part of the moisture could be removed, but absolutely dry it was quite impossible to 

 make the chamber. After a time the limpid salt water became replaced by a more sticky 

 fluid, which frothed with the violent efforts of the scaphognathite. Of course it is possible 

 that this was blood, flowing from wounds in the delicate cuticle lining the chamber, made 

 during the process of drying. But I was unable to detect any such wounds, and the 

 same thing happened in each of several experiments. Another explanation of the pheno- 

 menon is that the fluid was provided by exudation through the lining of the chamber. 

 No doubt in this case the exudation was abnormal in quantity and quality. But it served 

 to indicate a possible method of keeping the gills moist. In support of this is the fact 

 that specimens made approximately dry^ with cotton-wool and then placed in a dry wooden 

 box, lived, and remained in good health for weeks. No doubt, if the suggested process 

 of exudation takes place, the different species of the genus are dependent on it to different 

 extents. One would expect, for instance, that it would play a greater part in species 

 such as C. spinosus, which often live at some distance from the sea, than in C. rugosus, 

 which is generally to be found close to sea-water. 



The movements of the scaphognathite. On raising the forepart of the branchiostegite 

 of a Coenobita the plate on the second maxilla, to the movements of which the respiratory 

 current in water-living Decapods is due, will nearly always either be found to be in 

 motion or shortly begin to move. When the animal is placed in water, either fresh or 

 salt, it is easy to show, by means of a little carmine or other coloured fluid, that the 

 ordinary cun'ent is produced here also. It enters at the hind end of the branchial chamber 

 and between the last two legs, passes over the gills and through the narrow passage which 

 leads downwards and forwards from the upper part of the gill-chamber proper, and finally 

 issues under the antenna. I have not been able to observe a reversal of the current, such 

 as that described by Bohn^ in many Decapods. The meaning of the movement of the 

 scaphognathite when the animal is on land is not clear. It is possible that its object is, 

 by acting as a fan, to create a draught of air through the gill chamber. In considering 

 this view, however, we are met by the difficulty that there are often long pauses in the 

 movements, and that removal of the scaphognathite has no perceptible effect on the animal. 



' See below, p. 91. kill the animal. 



- See below, p. 91. i Bohn, C. Rend, cxxxv. p. 539. 



3 If the drying process be continued too long, it is apt to 



