INTERNAL DIFFERENCES 4.7 
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.! 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 Porcellanidz nor in the Gala- 
theidze 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. X\vili. 
