3*76 /S. J. Smith — Early Stages of the American Lobster. 



For convenience of -comparison, the detailed measurements of the 

 young- in these different stages are arranged together on p. 378. 



A comparison of the Larval stages of the European h>l)ster with 

 those of our own species would be very important and interesting, 

 but as fiir as 1 can learn, no complete figures or descriptions of the 

 larval stages of the European lobster after leaving the egg have been 

 published. Rathke's* figures of the embryo of the European lobster 

 just before leaving the Qgg,, indicate the base of the antennula as com- 

 posed of tliree distinct segments, the branchial appendages of the 

 external maxillipeds and the cephalothoracic legs as much further 

 advanced than they are in the first larval stage of the American 

 lobster described in this paper, and the appendages of the penul- 

 timate segment of the abdomen are already represented by small 

 lobes beneath the abdomen. In the same stage of the embryo, the 

 lateral spines upon the second to the fifth segments of the abdomen 

 have appeared, but no dorsal spines are indicated in the figures. 

 Kroyer'sf figures of the embryo, apparently at nearly the same stage 

 of development, represent some of the appendages veiy difierent. 

 The anterior cephalothoracic legs are represented as truly cheliform, 

 the lateral spines upon the segments of the abdomen are mistaken 

 for abdominal legs and represented as each composed of two seg- 

 ments, wdiile the telson is represented as quite difierent in form from 

 either Rathke's figures or from those of any stage which I have ob- 

 served in the American lobster. 



Of all the larval stages of other genera of Crustacea of which I have 

 seen figures or descriptions, there are none which are closely allied to 

 the early stages of the lobster. Astacus, according to Rathke, leaves 

 the egg in a form closely resembling the adult, the cephalothoracic 

 legs having iio exopodal branches and the abdominal legs being 

 already developed. Of the early stages of the numerous other genera 

 of Astacidea and Thalassinidea scarcely anything is known, but as 

 far as is known none of them appear to approach the larvre of the 

 lobster. Most of the species of Crangonida and PalaBmonida? — among 

 the most typical of macrourans — of which the development is known, 

 are hatched from the egg in the zoea stage, in which the five poste- 

 rior pairs of cephalothoracic appendages or decapodal legs are wholly 



* Beitrage zur vergleichenden Anatomie und Physiologie, uber die Riicksclireitende 

 Metamorphose der Theire, Danzig, 1842, p. 120, plate ii. 



f Monografisk Fremstilling af Slajgten Hippolyte's nordiske Arter, med Bidrag til 

 Dekapodernes Udviklingshistorie (Kongl. Danske Vidensk. Selsk. naturvid. og matliem. 

 Afhandlinger, ix Deel), Kjobenhaven, 1842, p. 251, plate vi. 



