THE MOUTH-PAKTS OF THE PALyEMONIB PRAWNS. 37 



4. On the Structure and Function o£ the Mouth-parts o£ 

 the Palsemonid Prawns. By L. A. Boreadaile, M.A., 

 F.Z.S., Lecturer in Zoology in the University of Cam- 

 bridge, Fellow, Dean, and Lecturer of Selvvyn College. 



[Received September 19, 1916 : Read February 6, 1917.J 



(Text-figures 1-51.) 



Index. Page 



Introduction 37 



Morphologj^ of the crustacean limb 37 



Morphology of the mouth-parts of Palasmonidae 62 



Physiology of the mouth-parts of Palffinionidse 69 



In the course of an investigation of the commensal prawns of 

 the subfamily Pontoniinee, it became necessary for me to compare 

 their mouth-parts with those of the free-living Palsemoniiufe, in 

 order to discover whether there existed between these groups 

 any difference, in the organs in question, which might correspond 

 with the difference in the diet of the animals. For the most part 

 I have taken as representative of the Palsemoninse the Common 

 Prawn {Leander serratiis), in which I have studied in some 

 detail the structure and arrangement of the mouth-parts, and 

 endeavoured, by the observation of living specimens, to find out 

 how the organs in question are used. Surprisingly little trace 

 has appeared of such structural differences between the sub- 

 families as I was looking for, but my observations have suggested, 

 with regard to the morphology and functions of the parts around 

 the mouth of Palfemonidse, certain reflections and conclusions 

 which form the subject of this communication. 



II. 



1. The morphology of the jaws of Malacostraca is still in a 

 good deal of confusion, and there is much disagreement as to the 

 relation of the parts of each of them to those of other crustacean 

 limbs, and even as to the names to be applied to certain of their 

 processes or "lacinise"*. A great part of this difiiculty arises 

 from the fact that no theory as to the primary form of limb of 

 which all the appendages of Crustacea are modified representatives 

 has met with general acceptance. This thorny question is not 



* I have not, in this summary article, made anj' reference to the literature of the 

 subject. The contributions of Beecher, Boas, Claus, Coutiere, Hansen, Huxley, 

 Lankester, Packard, Thiele, and others to our knowledge of homology of the limbs 

 of Crastacea are well known to those who are interested in the subject. The reader 

 will readily gather in what respects my views difl'er from or agree with those 

 expressed by each of them, and it is needless to emphasize the fact that all present 

 speculation must be based upon the foundation they have laid. 



