RESEARCH ON THE DIGESTIVE SYSTEM OF THE SCHIZOPODA 53 



Whilst external détails, — the first to be modified by external in- 

 fluences, — may be quite sufficient to dijferentiate forms that are closely 

 related, yet the internai structures, — which are not so easily modified, 

 — seem to be more important when we try to find ont the phylogenetic 

 relationship between externally différent types. 



Are we not, therefore, failing in scientific method when we build up 

 groups and subdivisions solely on the variations of external morphology 

 without carefuily examining the détails of their internai organisation? 



Physiology. 



1"' Œsophagiis. 



The food after being separated and divided by the mandibules and 

 maxillïE passes up the œsophagus into the anterior cavity of the stomach. 

 The longitudinal and circular muscle bands enable the œsophagus to per- 

 form peristaltic movements. 



The jnouth and œsophagus can be enlarged or reduced in size, and 

 the cardiac chamber can be brought nearer to the mouth by means of 

 strong muscular bands Connecting its walls with the external integument. 



2" Stomach. 



The physiological signification of the stomach in the Crustacea has 

 been much discussed. 



Are the plates which are found in the stomach powerful auxiliaries of 

 the mandibules and maxillae endowed with a masticating function, or is 

 their rôle simply that of mixing the food stuffs with the ferments secreted- 

 by the digestive glands, or hâve they an altogether différent function? 



Considering the structure of thèse pièces one would say at first sight, 

 that they were nothing more than an effective masticating apparatus. 



This, however, has been contested. 



The researches of Plateau on the crab seem to show that the pièces 

 in the cardiac chamber of this animal hâve only a very feeble masticating 

 power. 



The investigations of other authors support this opinion (Balbiani, 

 Weissmann, Miall). 



Another function has, therefore, been attributed to the stomach, viz. 

 that of a filter preventing the food stuffs from going further before they hâve 

 undergone the action of the digestive ferments. 



