Limbs and Mouth-parts of Crustaceans and Insects. 425 



with the fourth and fifth segments of the Mysid limb taken 

 togetlier. I derive this conclusion from the development and 

 direction of the articulations, and, moreover, 1 would point 

 out that a precisely similar condition is found in the Pseudo- 

 scorpions : for, in the first two pairs of limbs in Chiri'dium 

 (as 1 have proved with absolute certainty in Nat. Tidsskr, 

 3 R. Bd. x'lv., and in a paper at present in the press) the 

 femur is undivided; in CheUfer it is divided into alt short 

 " trochantin " and the true femur ; while in Garypus, and 

 still more in Ohisium^ tiie femur is differentiated into a long 

 pars hasalis and a short pars tibialis^, so that it is impossible 

 to determine the homology of the segments by means of 

 numbers {vide § 2). The maxillulte have lobes on the first 

 and third segments, and, in a certain larval stage, also on the 

 third segment, an exopodite, ichich subsequently disappears; 

 vihile the organ which in the adult animals is regarded as an 

 exojjodite by authors is a plate-like development of the first 

 segment, which appears later on f. The maxillse as regards 

 the origin of the lobes agree with the Mysidte. 



23. The Decaj)oda approach the Euphausiida very closely. 

 The second segment of the maxillulae 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 

 Euphausiidfw (Boas), but it follows from § 22 that the names 

 bestowed by H. I^lilne-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 uot disappear 

 in the Idotheida?, but forms a portion of the lateral region of 

 the body ; if ice assume that the first segment of the limbs 

 which has been described in the Fhyllopoda, but overlooked or 

 misunderstood by the majority of authors, likewise does not 

 disajipear, it consequently forms a larger or smaller portion of 

 tlie 2J^<^urib. This view seems to be capable of explaining the 

 fact that in the Decapods branchiae are found both upon the 

 pleural, upon the arthrodial membrane between the pleurae 

 and the limb, and also upon the coxopodite ; since the portion 

 of the pleurje provided with branchia; is to be regarded as 

 originally belonging to the limb, so that we now find its 

 vanished segment represented by branchiae alone. Compare 



* This latter condition must be regarded as the piiniiti\e one, and 

 therefore a fusion of segments takes place ; but for practical reasons I 

 have employed the expressions used. 



t ['k/cG. O, Sars ('Challenger' Keport), ^vho has figured this cor- 

 rectly, but given it a wrong interpretation ; vide also " L)ijmphna-Togtet." 



