Limbs and Mouth-parts of Crustaceans and Insects. 425 
with the fourth and fifth segments of the Mysid limb taken 
together. I derive this conclusion from the development and 
direction of the articulations, and, moreover, | would point 
out that a precisely similar condition is found in the Pseudo- 
scorpions: for, in the first two pairs of limbs in Chiridium 
(as I have proved with absolute certainty in Nat. Tidsskr. 
3 R. Bd. xiv., and in a paper at present in the press) the 
femur is undivided; in Chelifer it is divided into afshort 
“trochantin” and the true femur; while in Garypus, and 
still more in Obistwm, the femur is differentiated into a long 
pars basalis and a short pars tibialis*, so that it is impossible 
to determine the homology of the segments by means of 
numbers (véde § 2). The maxillule have lobes on the first 
and third segments, and, in a certain larval stage, also on the 
third segment, an exopodite, which subsequently disappears ; 
while the organ which in the adult animals is regarded as an ~ 
exopodite by authors is a plate-like development of the first 
segment, which appears later ont. The maxille as regards 
the origin of the lobes agree with the Myside. 
23. The Decapoda approach the Euphausiide very closely. 
The second segment of the maxillule is fused with the first, 
so that the lobes proceed from the first and second segments. 
The segmentation of the limbs is essentially the same as in 
Euphausiid (Boas), but it follows from § 22 that the names 
bestowed by H. Milne-Edwards upon the several segments 
cannot be employed without consideration in the case of the 
orders mentioned in §19 according to the number of each 
segment, with the exception of the first three. 
24. As shown in § 20, the coxopodite does not disappear 
in the Idotheide, but forms a portion of the lateral region of 
the body ; ¢f we assume that the first segment of the limbs 
which has been described in the Phyllopoda, but overlooked or 
misunderstood by the majority of authors, Wkewise does not 
disappear, it consequently forms a larger or smaller portion of 
the pleure. ‘This view seems to be capable of explaining the 
fact that in the Decapods branchiz are found both upon the 
pleure, upon the arthrodial membrane between the pleure 
and the limb, and also upon the coxopodite ; since the portion 
of the pleure provided with branchiz is to be regarded as 
originally belonging to the limb, so that we now find its 
vanished segment represented by branchie alone. Compare 
* This latter condition must be regarded as the primitive one, and 
therefore a fusion of segments takes place; but for practical reasons [ 
have employed the expressions used. 
+ Vide G. O. Sars (‘ Challenger’ Report), who has figured this cor- 
rectly, but given it a wrong interpretation ; vede also “ Dijmphna-Togtet.” 
