1386 CRUSTACEA. 



still stronger support to this view. Kroyer has figured the youno* of 

 several species in his Tidsskrift, vol. in., and has given other figures 

 in the Crustacea of the Scandinavian Voyage. The early youn°- have 

 three pairs of appendages, like those of Caligus and the Cyclopoidea • 

 and as in those groups, the first pair is evidently second-antennary. 

 The figures show that it is plainly anterior or superior to the trunk 

 or mouth. Moreover, the organs have the chelate form found in 

 adults, so that there is no doubt as to their being the same organs in 

 the two. 



The common idea that these organs are mandibular is unsustained by 

 any observations. Before admitting this as their character, it would 

 be necessary to discover that the base or a process from it contributes 

 to the mandibular function within the trunk. But of this there is no 

 proof, and more than this, there is no reason to suspect it. There is 

 no instance of a mandible becoming so completely a leg, as to lose 

 wholly the mandibular function, even of its basal portion ; this would be 

 a violation of analogy. Even in Limulus, where the transformation 

 of the mandible is most complete, the basal joint retains the mandi- 

 bular character. Neither have we better evidence that the organs 

 are maxillary. 



The second pair of appendages arises from alongside of the first, and 

 so closely upon the same base, that one has been called the palpus 

 to the other. In some cases the cephalic segment projects either 

 side, like the thoracic segments, and upon this projection or com- 

 mon base stands the chelate organ and its so-called palpus; and 

 Goodsir figures a species, which he calls Pephredo capillata, with the 

 palpus arising from the side of the first joint of the chelate branch.* 

 There is reason, therefore, for considering the second organ as a part 

 of the first, and so we deem it. It appears to be the accessory branch, 

 similar to what occurs in many Cyclopoidea and other Entomostraca. 

 In Argulus, there are the two branches similarly related; the ante- 

 rior is prehensile and like the second antenna in Caligus, while the 

 posterior is palpiform. 



We therefore conclude, that both organs are parts of a pair of 

 antennas, and normally the second antennas, those of the first pair, as 

 in Argulus, being wanting. 



The third pair of appendages of the same segment, are evidently 



* Jameson's Jour., xxxii. pi. 3, fig. 9. 



