Zoology. 141 



Dr. Strahl proposes new names for the first two joints of the external 

 antenn?e ; the first (coxocerite) he would call intercalare ; the second 

 (basicerite) armiger ; while the third (ischiocerite), he calls the first joint 

 of the antennse, which is certainly liable to mislead. Professor Milne- 

 Edwards, who has done so much towards elucidating the homologies of 

 these joints, has given to them the names in brackets, which are more 

 appropriate ; for there is undoubtedly a perfect correspondence between 

 them and the joints of the maxillse or feet. I believe it possible to carry 

 the homology even further than the celebrated French zoologist has 

 done, and that the antenna in question, like a foot or maxilliped, con- 

 sists normally of seven joints. In the embryo of Hippolyte as figured by 

 Kroyer (Monog. Fremst. af Hippolyte 's Nordiske Arter, etc., tab. vi, f. 

 121), there are five distinct joints beyond the basicerite, which would 

 make seven in all. Moreover they can be demonstrated in the adult 

 Squilla, Axius, and Pagurus, and particularly well in Homarus, where 

 the parts are more distinct from their large size. The "peduncle" of 

 the antenna in the lobster is considered by Milne-Edwards to consist of 

 five joints; but a sixth is indicated at the base of the. penult, on the 

 lower side of the member. Here there is a small triangular piece, 

 articulating with the second and third joints as well as the penult, per- 

 fectly mobile, and dependent upon no one of these joints more than 

 another. An additional evidence that this piece is the representative of 

 a distinct joint is furnished by the fact that the articulations of the two 

 proximate joints are in the same plane, and not, as should be the case 

 were they normally contiguous, in planes perpendicular to each other. 

 To complete the number (seven) of joints we have the flagellum, which 

 corresponds to the dactylus or terminal joint of the thoracic members. 

 This homology is rendered probable by the occurrence, in the remark- 

 able Hippidean genus Mastigopus* discovered by me in the Chinese 

 Seas, of a multiarticulate dactylus to the chelipeds perfectly similar to 

 the flagelliform terminal appendage of an antenna. 



The squamiform appendix of the antenna is attached to the second 

 joint, and is homologous to the exopod of the feet, or the exognath of 

 the maxillipeds, which has the same position. It is called scaphocerite 

 by Milne-Edwards, but would be more appropriately named exocerite, a 

 term indicating its relations with greater exactness, and corresponding 

 in construction with that of its homologues. This appendage is normally 

 two-jointed, as is seen in the embryo Homarus and in the adult Squilla; 

 its basal joint is obsolete or coalesced with the terminal squamiform 

 joint in adult Macroura and Anomoura, while in Brachyura the entire ap- 

 pendage disappears with perfect development. The little basal joint of 

 the exocerite in embryo Homarus is mistaken for the "armiger" (basic- 

 erite) by Dr. Strahl, who considers the large joint which supports both 

 branches of the antenna as the " intercalare" (coxocerite), on the ground 

 that in the adult the third joint is articulated with both the coxocerite 

 and the basicerite. But this is so only in appearance ; — if the antenna 

 in a fresh lobster or cray-fish be bent outward, it will be seen that the 

 posterior condyle of the third joint articulates with the basicerite alone. 



2 Proc. Acad. Nat. Sci. Philad., Dec, 1858. Not the Mastigopus of Leuckart, 

 ■which is a Sergestes. 



