212 EVENINGS AT THE MICROSCOPE 



moreover, both were but the early states of well-known 

 and familiar forms of larger Crustacea, which therefore un- 

 dergo a metamorphosis as complete as that by which the 

 caterpillar changes to a chrysalis, and the chrysalis to a 

 butterfly, and in every essential point parallel to it. 



In the Cove of Cork this naturalist met with a consid- 

 erable number of Zoeas, which he kept in captivity. Some 

 of these passed into the Megalopa form, which in turn 

 changed to the most abundant of our larger Crustacea, the 

 common Shore-crab (Carcinus mcenas). "Thus, in its prog- 

 ress from the egg to its final development, the Crab was 

 proved to pass through two temporary conditions, which 

 had previously been regarded as types, not of genera only, 

 but of different families; and both strikingly dissimilar 

 from the group to which, in its perfect state, it belongs." 



I have not myself examined the transformations of this 

 species; but, as they have been well worked out, and as 

 the animal is so abundant everywhere on the coast that 

 you may easily verify what has been observed, I will cite 

 you the elaborate account of Mr. E-. Q. Couch of Pen- 

 zance, who has investigated the subject with great skill, 

 zeal, and success. 



Having procured some specimens of the Shore-crab 

 laden with eggs, just ready for shedding, he goes on to 

 say "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 num- 

 bers 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 cap- 

 tive Crabs. In order, however, to secure accuracy of re- 

 sult, one of the Crabs was removed to another vessel, and 



