MR. LUBBOCK ON SOME FRESHWATER ENTOMOSTRACA. 209 
the composition of the six posterior legless segments is a sufficient refutation of any 
such idea. 
Moreover Prof. Milne-Edwards considers that in the branchial feet of the Phyllopods 
one can distinguish “trois portions principales ou branches qui semblent représenter 
les trois parties qui chez les Décapodes constituent la tige principale des pattes ou des 
pattes-máchoires, le palpe et le fouet; mais ici toutes ces parties sont lamelleuses." Now, 
if this is true of the anterior legs in Apus, it is true of all; for they all consist of the 
same parts, however much they may be reduced in the posterior pairs. 
But even if we were to admit Prof. Dana's theory, it would not remove his difficulty. 
The appendages of Apus are, first, the eyes; secondly, the antennæ ; then the mandibles 
and two pairs of maxillze, which of course represent five segments, to which we must add 
one more for the second pair of antenne. Now, if we divide the sixty pairs of legs by 
three, we shall still have twenty leg-bearing segments, which, added to the anterior 
. ones, gives a total of twenty-six; and as Prof. Dana has adopted the theory of Milne- 
Edwards and Audouin, that the body of a Crustacean consists normally of only twenty- 
one segments, he has still five intruders for which his hypothesis does not account. 
But why should we be called on to account for the number of segments in certain 
Branchiopods? The same character occurs in the Crustacea of the earliest geological 
periods. In fact the Branchiopods hold the same position with reference to the 
Crustacea as the Myriapods do with reference to Insects. In conjunction with certain 
special characters of the Crustacea in the one case, of the Insects in the other, they 
retain the general Annulose characteristic, of a variable and often great number of 
similar segments. 
We see therefore that the two principal divisions of the Articulata, the Insecta and 
Crustacea, were already differentiated before the number of segments was limited so 
strictly as we now find it to be; and we are, I think, thereby led to the conclusion that 
the posterior segments of Apus and its allies have no representatives in the higher 
Artieulata. The body of a Lobster, in fact, corresponds not to that of a mature, but of 
a young Apus; and the forces, perhaps, which in the first have produced a high degree of 
differentiation have in the other spent themselves on an almost irrelative repetition. 
