204 



Mr. G. Brook on the Rate of Development 



In Mr. Spence Bates's figure of the pleopoda of the Megalopa 

 the last pair are not drawn correctly, unless the specimens I 

 observed were abnormal. The pleopoda usuallj consist 

 of two joints, the basal one of which has a protuberance 

 on the inner margin, while a large number of fine bristles 

 arise from the apical portion of the long spathulate terminal 

 joint ; but the last pair consists of two short thick joints, with 

 only five strong bristles arising from the terminal joint (see 

 fig. 1 a). Thus even in the Brachyuran larva there is an 

 indication of the fan-like plates into which these appendages 

 are developed in the Macrura. 



The Megalopa-stage from Redcar was collected on the 

 25th of August, 1883j and below I give a list of the moults 

 already gone through for two individuals. I had five alto- 

 gether, and four out of the five followed the moults of A 

 within a day or two so long as they lived ; while B, which 

 seemed somewhat a retarded specimen in its earlier moults, 

 is now a fine young crab with a carapace 12*4 millim. long 

 and 15'5 millim. broad. 



A. 



Ecdj'sis to adult form 



1st ecdysis 



2nd „ 



3rd „ 



4fch „ 



6th „ 



6th „ 



7th „ 



8th „ 



26. 

 5. 

 20. 

 16. 

 14. 



VIII. 



83 

 IX. 



83 

 IX. 

 "83" 

 I. 

 83 

 XII. 

 83 

 III. 

 84 



dead. 



In the Plate will be found drawings of the Megalopa and 

 the first six ecdyses of form B, drawn to scale, so that a 

 careful comparison may be made of the whole series. 



Fig. 2 represents the form assumed after Jeaving the Mega- 

 Zo^a-stage. The carapace is still a little longer than broad ; 

 the rostrum continues to occupy about one fifth of the whole 

 area of the carapace, but the frontal spine has been lost, and 

 is now only represented by a slight undulation. This margin 



