OF CRUSTACEA. 



279 



insulate and preserve alive these almost imperceptible crea- 

 tures, until they attain to their full growth as Zom, we cannot 

 calculate upon ever tracing them during the whole of their 

 progress. However, it is by no means unlikely that the Zoea 

 being captured in their adult state, may be observed in the act 

 of passing into the second form of Megalopce, as very nearly 

 happened in the instance given in Zool. Res. p. 8. We 

 must, until then, be satisfied with the facts detailed in the 

 Memoir on Carcinus, where it is clearly shown that Megalopa 

 is an intermediate stage between Zoe and the perfect crab, 

 and from which we have every reason to presume that the same 

 prevails with regard to the other genera of which we have not 

 an equally clear chain of evidence. These facts first became 

 known on the 8th of June, 1827 ; and on the 14th of the 

 same month, 1 obtained the Megalopa (fig. 3,) which, from the 



Fig. 3. 



structure of its hind feet, is evidently that of a Portunus. It 

 would be presumptuous, however, to say that it is that of the 

 identical species of which the above-described Zoe is the larva, 

 although it is not improbable from P. marmoratus being the 

 most common species. 



