166 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY. 



EXPLANATION OF THE PLATES. 



PLATE I. Carcinus meenas. 



Embryo beginning to emerge from the egg. 



The same, a little further along. 



Embryo shortly after hatching. 



First antenna of the same. 



Second antenna of the same. The branch (3) invaginated : <x', spine 

 of the antenna of the zoea seen through the cuticle ; b', squamiform ap- 

 pendage of the antenna of the zoea. 

 Fig. 6. Tail of the same : the enclosed tail of the zoea is shaded ; spines 2, 3, and 

 5 are invaginated. 



The same : all the spines of the embryonic tail evaginated. 



Invaginated rostrum of the zoea, as seen through the embryonic cuticle. 



Young in the act of exuviating the embryonic cuticle. 



The cuticle of the abdomen, just cast from Fig. 9. 



Second antenna of the zoea : a, spine ; b, squamiform appendage ; c, rudi- 

 ment of the flagellum of the adult. The spine and squamiform append- 

 age are still invaginated. 



To show the way the dorsal spine lies at the time of the first moult. It 

 has become evaginated, but not yet erected. 



Extremity of a prong of the caudal fork, to show the unfolding of the dis- 

 tal part, and the terminal hook. 



Eostrum and antennse of a zoea at the moment of exuviating the embry- 

 onic cuticle. 



Dorsal spine of zoea immediately after casting the embryo skin. The 

 break near the middle of the spine shows the rim of the invagination 

 during the earlier period. 



PLATE II. 

 Figs. 1-3. Carcinus maenas, 



o 



Fig. 1. First stage of the zoea. The appendages are marked by consecutive Roman 

 numerals. 

 Tail of the same. 

 First and second antennse of the same. 



Figs. 4- 10. Panopeus Sayi. 



First stage of the zoea. 

 The same, viewed from behind. 

 Tail, with the embryonic cuticle. 

 First antenna of the embryo. 



Second antenna of the embryo : a', antenna of the zoea seen through the 

 embryonic antenna. 

 Fig. 9. Second maxilla of embryo. The shaded part represents the appendage of 



the zoea within. 

 Fig. 10. End of swimming-branch of first maxilliped. The long swimming-setse are 

 shortened by invagination and closely invested by the embryonic cuticle. 

 Fig. 11. Tail of Gelasimus pugnax, Smith, first stage of the zoea. Spines 5, 6, 7, 

 are entirely wanting. 



