MUSEUM OF COMPARATIVE ZOOLOGY. 165 



Panopeus Sayi. 



The remarkable zoea represented on Plate II. Fig. 4, a very common 

 form on the southern shore of New England, I raised from the eggs of 

 Panopeus Sayi in the summer of 1876. It differs strikingly from all 

 other zoese with which I am acquainted in the structure of the second 

 pair of antennse (ii.), which consist of a single monstrously developed 

 spine equal in length to the rostrum. In other regards the zoea is not 

 specially noteworthy. The carapace has, in addition to the rostral and 

 dorsal spines, a pair of short lateral spines. In the middle line of the 

 back, well forward toward the eyes, is a well-marked hump. 



The caudal fork (Fig. 5) bears but four pairs of spines ; the two exte- 

 rior pairs (6 and 7 in Garcinus) are wholly wanting. 



To which part of the typical second antenna of the zoea, as described 

 on page 162, does the long, rod-like antenna in this species correspond % 

 In order to answer this question we must examine the cuticle of the 

 embryo. This is represented by Fig. 8 of the plate. It has a form 

 similar to that previously described in Carcinus mcenas (PI. I. Fig. 5) ; 

 but here the branch marked 3 is split nearly to the base, making an ap- 

 parently quadruple structure in place of the triple branch of Carcinus. 

 The blunt, finger-like process (a) encloses the antenna of the zoea (a'), 

 which is marvellously shortened by evagination. The homology of the 

 zoea antenna in this case is thus fixed. It represents the spine of the 

 normal antenna. 



The cuticle covering the first pair of antennae (Fig. 7) has the same 

 parts as the corresponding structure in Carcinus, and the same with the 

 tail (Fig. 6), in which the two external spines (6 and 7), which are en- 

 tirely wanting in the first stage of the zoea, are well developed. 



Cambridge, July, 1880. 



