52 Charles GELDERD 



Thèse are accessory, therefore, and do not belong to the typical pièces. 



The Schizopoda ressemble the Decapoda in having no direct opposi- 

 tion between ail the pièces of the same side of the stomach. 



In the Schizopoda and Decapoda it seems to us that the pièces of the 

 cardiac chamber are more highly developed as prominent reliefs, precisely 

 to ensure opposition between the corresponding pièces of the opposite side. 



Comparing the two chambers of the stomach in the three groups, it 

 seems to us that it is the pyloric chamber which suffers the least in struc- 

 tural modification. 



In the Schizopoda and Decapoda the cardiac chamber is distinctly 

 separated from the pyloric chamber. 



This is not the case in the Edriophthalmia. 



MocQUART came to the conclusion that the study of the gastric skeleton 

 of the Podophthalmia was an important élément in determining the natural 

 affînities in this large section of the Crustacea, on the principle that this 

 apparatus is less under the influences of the external causes of variation. 



This seems most reasonable, for the causes which hâve brought about 

 external différences during successive adaptations to varions conditions of 

 environment were mostly external also. 



It is but natural, therefore, to suppose that the external morphology 

 should be more subject to thèse outside influences. 



It is but natural, also, to suppose that the internai organisation should 

 hâve been more respected for it is less exposed to thèse causes of variation. 



Of the two chambers of the stomach, we should expect to find the 

 anterior chamber more exposed to external influences, and therefore more 

 subject to variation in the différent species and groups, than the posterior 

 chamber. 



This is what we find to be the case in comparing the groups of Schizo- 

 poda, Edriophthalmia and Decapoda. 



It is, however, upon the external morphology of the Arthropoda, 

 which is the most subject to variation, that even some récent Systems of 

 classification are almost exclusively based. 



A classification should express the phylogenetic relationships of the 

 groups and species as far as that is possible. Are we justified, therefore, in 

 totally neglecting at the présent day the variations in the internai organi- 

 sation in the study of the afhnities and in the hypothetical establishment of 

 the différent groups of Arthropoda? 



