162 BULLETIN OF THE 



appendage of Spence Bate), of the enclosed zoea. The flageUum of the 

 antenna of the adult, seen in the first zoea stage as a small protuberance 

 (PI. I. Fig. 10, c), has no representative in the embryonic antenna. The 

 spinous process and scale of the zoea antenna are much shortened by 

 invagination, like the structures of the tail already described.* 



Morphology of the Antennce. — One can hardly avoid the conclusion 

 that, in the same way that the seven-spined forked tail of the embryo is 

 a reminiscence of the Gabelschwantz (P. Mayer) of the primitive Deca- 

 pod, so the greatly developed, setiferous antennae are an inheritance 

 from ancestors in which these appendages subserved locomotive func- 

 tions, as in the Naiiplius. The typical second antenna of the Zoea con- 

 sists of a basal stem produced at its distal end into a long serrate spine 

 (PI. I. Fig. 10, a ; PI. II. Fig. 3, ii. a), and bearing besides an articulated 

 squamiform appendage (6). The spine is seen in a rudimentary form in 

 the larvse of the shrimps, prawns, and Paguridce. The squamiform ap- 

 pendage is homologous with the external branch of the second antenna 

 of the larval Macroura, and with the antennal " scale " of the adult 

 Macroiira. Both the spinous process and the squamiform appendage 

 become aborted in the development of the Brachyura. The flagellum of 

 the second pair of antennso of the adult crab is wanting in the youngest 

 zoea stages, or is represented by a small papilla merely (c). 



If the relation of the embryonic antenna to the Nauplius antenna, 

 suggested above, be correct, it follows that the bulk of the antenna of 

 the Naicplius is not represented by any homologous part in the perma- 

 nent antenna of the crab. If, on the contrary, it be claimed that the 

 large fringed lobes of the embryonic antennee simply represent antennal 

 setre, they still point back to a primitive condition in which the first two 

 pairs of appendages were provided with Schwimborsten, and served as 

 natatory organs. 



The labrum, mandibles, metastoma, and maxillae have nearly the same 

 form which they have in the zoea stage which follows. The long swim- 

 ming-setae of the first and second maxillipeds, which play so conspicuous 

 a part in the life of the zoea, are very much shortened by invagination, 

 and entirely covered by the embryonic cuticle. 



The third pair of maxillipeds and the two following pairs of appen(Jages 

 of the zoea show through the transparent membrane as three pairs of 

 small buds (PI. I. Fig. 3, viii., ix., x.), but there are no corresponding 

 structures in the embryo. 



* A. Dohrn, who observed similarly formed antennae in the embryo of a species of 

 Portunus {I. c. ), has confounded the two pairs. 



