1898.] POST-LARYAI STAGES OF THE COMMON CBAB. 205 



TJ.S. Eish. Comm. Eep. 1871-72, published in 1873, gives some 

 observations on the early stages of the ximerican species Cancer 

 irroratus. He states that Zoseas of the species were taken 

 abundantly in Vineyard Sound from June 23rd till late in August. 

 Megalopas were also taken, and that the change of the Megalopa 

 into the first crab-form was observed in aquaria. In this early stage 

 the young Crab was quite different from the adult. The carapace 

 was about 3 rain, long and slightly less in breadth. The front 

 was much more prominent than in the adult. The antero -lateral 

 margin was much more longitudinal than in the adult, and was 

 armed with 5 normal teeth, which were long and acute, and 4 much 

 smaller secondary teeth alternating with these. Young Crabs in 

 this stage were once or twice taken in the tow-net. figures of 

 the Zosea and Megalopa are given, but none of the first crab-form. 

 The most important part of this description in relation to my own 

 observations is that concerning the teeth on the antero-lateral 

 margin. 



During last summer, while engaged in presenting to Cornish 

 crab-fishermen the known facts concerning the natural history of 

 the animals it is their business to capture, I endeavoured, when 

 leisure and opportunity allowed, to trace the successive stages of 

 the Edible Crab in the littoral waters. Having failed to identify 

 any of the stages in the produce of the tow-net, or to obtain any 

 stages later than the Zoaea hatched directly from the ovum, I 

 began to search the shore at low tide in the hope of finding the 

 earliest ambulatory stages derived from the swimming larvae 

 hatched some weeks earlier. This search was also for a time 

 unsuccessful, but at the Laboratory of the Marine Biological 

 Association at Plymouth I obtained on Sept. 28th the specimens 

 which form the subject of the present paper. They were found 

 among a quantity of coralUne growth collected on the shore at 

 Wembury Bay and were examined in the Laboratory, and my 

 possession of them is due entirely to the exertions made by the 

 Director and his assistants on my behalf. 



The specimens were ten in number, the smallest 2-5 mm. across 

 the carapace, the largest 7 mm. The largest specimen was quite 

 similar to the adult Cancer pagurus. Two or three of the smallest 

 specimens had the characters shown in fig. 1 (Plate XXI.), while the 

 rest were in a condition intermediate between this and the ordinary 

 condition of Cancer prt^wrtts. One of the most typical of these 

 intermediate conditions is shown in fig. 2 (Plate XXL), drawn 

 from a specimen 4 mm. in breadth of cai'apace. 



Eor a time it seemed doubtful whether the smallest specimens 

 as represented in fig. 1 were the young of Cancer pagurus or of 

 Atelecyclus Tieteroclon, as the antero-lateral teeth of the carapace are 

 so similar to those in the adult condition of the latter species. 

 The specimens seemed, however, to belong to the same series, and 

 the facts that the outline of the carapace is not so regularly 

 circular in the smallest specimens as in Atelecyclus, and that no 

 more advanced specimens of that species were found in the 



