INTRODUCTION. xlix 



sioned it to be more fully investigated than any other; 

 and it may, therefore, be taken as the type of the process 

 amongst the Brachyura. Thus it was the first form in 

 which the Megalopoid period was observed by Mr. 

 Thompson ;* it was four years afterwards described in its 

 zoeform state by Capt. du Cane, who, it appears, was not 

 acquainted with Mr. Thompson's paper; it has occupied 

 tlie attention of Mr. H. Goodsir; and it forms the subject 

 of Mr. R. Couch's elaborate and very complete re- 

 searches. To the latter of these, as embodying all that 

 is at present known on the subject, and as being the 

 result of the personal observation of so intelligent and 

 acute an observer, I shall have recourse for the general 

 description of this process in the Brachyura. In the first 

 place it appears that Mr. Couch met with the young Zoes 

 already hatched; and even then he had the satisfaction of 

 finding them pass into the Megalopoid condition described 

 by Thompson. Afterwards, however, he procured some 

 specimens of the crab itself laden with ripe ova, just 

 ready for shedding; and he then proceeds with the 

 account of his observations: — 



" These were transferred to captivity, placed in sepa- 

 rate basins, and supplied with sea water, and in about 

 sixteen hours I had the gratification of finding large 

 numbers of the creatures alluded to above, swimming 

 about with all the activity of young life. There could be 

 but little doubt that these creatures were the young of 

 the captive crabs. In order, however, to secure accuracy 

 of result, one of the crabs was removed to another 

 vessel, and supplied with filtered water, that all insects 

 might be removed ; but in about an hour the same crea- 

 * Phil. Trans, ut supra. 



