6 L. A. Borradaile — Coral-Gall Prawn Paratypton 



is nothing which strongly suggests a diet of plankton. 

 Certainly there is no conspicuous apparatus for gathering it, 

 though possibly both here and in some Pontoniinae the broad 

 third maxilliped may be of use by forming a wall to the mouth 

 region and thus enabling finely divided food to be kept under 

 control. The peculiarities of the maxillules are probably 

 connected with those of the metastoma, but what their effect 

 may be it is impossible to say. The most striking features are 

 those of the mandible, and here there is probably a definite 

 adaptation to some specific food. But there is nothing to show 

 that that is plankton. For information on this point we must 

 wait till further knowledge of the habits of the prawns, and 

 of the structure of their galls, shall have been gained. There 

 are several possibilities. The openings of the galls are prob- 

 ably small, but we are quite in the dark on this point, 

 and it may be that the prawn receives relatively large morsels 

 of food through the agency of its stream. Or, it may be that 

 the animal feeds, as Hapalocarcinus was formerly supposed to 

 feed, on the fleshy parts of the coral, which in that case must 

 regenerate rapidly. Or, again, it may be that Paratypton has 

 some means, not obvious when it is not feeding, of gathering 

 the nannoplankton. Possibly it may live, as certainly does 

 the crab Melia which carries anemones in its chelae, by 

 stealing food caught by the polyps. If this be accompanied 

 by mucus, thesurprisingly normal character of the mouth-parts 

 of the prawn could be accounted for in the same way as that 

 of the same organs in Pinotheres, commensal with bivalve 

 molluscs, and probably also of those Pontoniinae which have 

 a like habitat. In these organisms the food is not in fact 

 finely divided, but consists of the strings of mucus with 

 entangled food which the host is forming for its own nourish- 

 ment. 



The legs are rather short and stout, with rounded joints, 

 which have no spines or sharp angles, and for the greater part 

 of their length bear sparsely a few short hairs, though at the 

 ends of the propodites these structures are longer and more 

 numerous. This reduction of the hairs of the legs, many of 

 which are undoubtedly tactile, is a part of the degeneration of 

 the sensory apparatus in sedentary Crustacea; and, taken in 

 connection with the clumsiness of the movements of such 

 animals when they are removed from their hiding-places, lends 

 support to Doflein's suggestion that it is a function of the 

 tactile hairs of Crustacea to enable their possessor to co- 

 ordinate the movements of its limbs. They would naturally 



