26 LEPAD1D.E. 



informed on the high authority of Mr. J. D. Dana,* 

 that this is the case with the cephalo-thorax in some true 

 Crustaceans, for instance, in Sapphirina. To proceed, 

 the mouth, formed of mandibles, maxillae, and outer 

 maxillae, correspond with the fourth, fifth, and sixth 

 segments of the archetype Crustacean. Posteriorly 

 to the mouth, we come, in the larva, to a rather wide 

 interspace without any apparent articulation or organ, 

 and then to the thorax, formed of six segments, bearing 

 the six pair of limbs, of which the first pair differs slightly 

 from the others. The thorax is succeeded by three small 

 segments, differently shaped, with the posterior one alone 

 bearing appendages ; these segments, I cannot doubt, 

 from their appearance alone, and from their apparent 

 function of steering the body, are abdominal segments. 

 If this latter view be correct, the thoracic segments are 

 the six posterior ones of the normal seven segments, and 

 there must be two segments missing between the outer 

 maxillae and first thoracic pair of legs, which latter on this 

 view springs from the ninth segment. Now, in a very sin- 

 gular Cirripede, already alluded to under the name of 

 Proteolepas, the two missing segments are present, the 

 mouth being actually succeeded by eight segments, and 

 these by the three usual abdominal segments, — every 

 segment in the body being as distinct as in an Annelid : 

 hence in Proteolepas, adding the three segments for the 

 mouth and three for the carapace, we have altogether 



* This distinguished naturalist has given his opinion in the ' American 

 Journal of Science/ March, 1846, that " the pedicel of Anatifa corresponds 

 to a pair of antennae in the young ;" although the peduncle or pedicel is 

 undoubtedly thus terminated, even in mature individuals, I think it has been 

 shown that it is the whole of the anterior part of the larva in front of the 

 mouth, which is directly converted into the peduncle. Professor E. Forbes, 

 in his Lectures, and Professor Steenstrup, in his ' Untersuchungen iiber das 

 vorkommen des Hcrmaphroditismus in der Natur/ ch. v, have considered 

 the peduncle as a pair of fused legs. Loven has taken, judging from a single 

 sentence, the same view of the homologies of the external parts as I have 

 done ; in his description of Alepas squalicola, (Ofversigt of Kongl. Yetens., 

 &c, Stockholm, 1844, pp. 192-4), he uses the following words : " Capitis 

 reliquse partes, ut in Lepadibus semper, in pedamulum mutates et invo- 

 ucrum" &c, ; his involucrum is the same as the capitulum of this work. 



