INTERNAL DIFFERENCES 47 



while the posterior portion represents its appendages. 

 This idea is still more strongly suggested in the genus 

 Cheiroplatea, where the separation of the posterior from 

 the anterior division is clearly defined by a distinct mem- 

 branous articulation, and the posterior portion is divided 

 into two lateral lobes.' 1 The older genus Porcellana is 

 even more to the purpose than Cheiroplatea, and Miss 

 J. M. Arms, in the Manual before referred to, considers 

 that it settles the question. Comparing a species of it with 

 the lobster, ' This curious little crab,' she says, ' possesses 

 a telson with an unmistakable pair of appendages attached 

 to it, proving that this part is really a ring whose appen- 

 dages are wanting in the lobster.' It must, however, be 

 remarked that neither in the Porcellanidte nor in the Gala- 

 theidge do these apparent appendages of the telson ever 

 become freely articulated with it, and as they are the last 

 to put in any appearance at all, and then only in a late 

 stage of the animal's development, it remains a question 

 whether they may not be dividing lines of the telson 

 rather than appendages arising from it. 



In the internal organs of crustaceans the differences 

 are as great as in the external. One writer has even 

 undertaken to classify the Brachyura according to the 

 structure of their stomachs. Unless this part of the 

 organism were tolerably complicated, it will be easily under- 

 stood that it would not afford sufficient variations for such 

 a purpose. But though, for establishing a really natural 

 system, every stage of an animal's development and all its 

 parts ought to be studied and taken into account, surely 

 a systematist ought to aim at founding his classification 

 as far as possible on the most accessible stages and the 

 parts most easily observed. At any rate the general 

 student will have little inclination to arrange his collec- 

 tion by investigating; in the different specimens the walls 

 of the stomach and the teeth and hairs within it, although 

 he may occasionally be pleased to observe in that of the 

 lobster the three horny-looking grinders, the central one 



1 Spence Bate. Report on the Macrura collected by H.M.S. Chal- 

 lenger, p. xlviii. 



