56 Papers from the Department of Marine Biology. 



Hapalocarcinus. A full account of the phenomenon has never been 

 given, even for such common forms as Daphnia and Simocephalus. A 

 short paper by Hartog and a few excellent observations by Woltereck 

 comprise the sum of publication. 



In such a form as Daphnia a current is constantly produced for respi- 

 ration and feeding by the movement of the thoracic appendages. This 

 current enters the space between the valves anteriorly and flows back- 

 wards ventrally; then turning upwards, comes in a reversed direction 

 along the ventral groove to the mouth. The small organisms in it are 

 collected beneath the labrum. The mandibles, which are palpless, 

 unlike those of Hapalocarcinus, have a broad triturating surface cov- 

 ered by a number of longitudinal ridges beset with short processes. 

 They are constantly in rhythmic motion, rubbing against each other 

 and to enter the gut every particle must pass between them and be 

 ground still finer. Mr. J. T. Saunders, of Christ College, Cambridge, 

 has pointed out to me that the food of these creatures is the "nanno- 

 plankton" and Woltereck states that in his experience small alga? 

 are the food supply. But, however minute the organisms on which 

 Daphnia feeds may seem to be, they are subjected to a trituration 

 which reduces them to an amorphous condition. The crushed frag- 

 ments are then sucked in by the peristaltic action of the gut. In 

 most animals the intestine is entirely filled with material in which it 

 is difficult to detect any structure. 



In briefly comparing, then, the feeding methods of Hapalocarcinus 

 and Daphnia and the consequent effects upon structure, it must first 

 be stated that both animals live on the smaller elements of the plank- 

 ton, probably mostly the "nannoplankton." The reduction of the 

 maxillae in both forms is in some way associated with this fact. But 

 there is a marked difference in the treatment of the diet; for while 

 Hapalocarcinus possesses no effective organs of mastication, only pre- 

 venting the access to the mesenteron of particles of too large a size by 

 means of a sieve, Daphnia subjects every organism entering its small 

 mouth to a thorough trituration by the very effective mandibles, 

 appendages which differ entirely in structure from those of Hapalo- 

 carcinus, only agreeing, in fact, in the absence of a palp. 



THE FEMALE AND ITS VARIOUS STAGES OF GROWTH. 



The colouration of the living female has never been described before, so 

 far as I know. In the younger females it is a light grey in gross effect. 

 If examined with a good lens a great number of small yellow-brown 

 spots are seen and between them branching white chromatophores. 

 In the older females the grey is much intensified, so that the crab 

 becomes the colour of lead. 



When a crab is liberated from a gall it creeps about with surprising 

 slowness. If a branch of coral be offered it, it clings to it with the 



