326 MR. WESTWOOD ON THE SUPPOSED EXISTENCE 



These circumstances are, I trust, amply sufficient to prove that the land Crab 

 does not undergo any metamorphosis. 



It is to be observed that Mr. Guilding has not stated the precise species of land 

 Crab of which the above-mentioned individuals were the offspring ; but his well- 

 known acquirements in crustaceology put the question of its being at all events a 

 species of land Crab to rest. Should this, however, be nevertheless called in ques- 

 tion, the argument which I would deduce from it will be but little diminished even 

 were it a sea Crab. 



We have seen that Mr. Thompson's supposed full-grown Zoe, which died on the 

 point of undergoing its supposed metamorphosis, was 3 lines long between the points 

 of the spines, and the length of which, from the head to the tail, must have been at least 

 1§ line. But the young of the common Crab is found of a much smaller size than 

 this, exhibiting at the same time all the form of the full-grown Crab. I have myself 

 captured the young of Cancer Mcenas not more than § a line long, yet perfectly 

 formed, and capable of running about with much quickness. 



Although disagreeing with Mr. Thompson in respect to his theory, I have already 

 stated that his figures are very faithful delineations of nature. I have therefore the 

 more pleasure in stating that his representations of the young of My sis are (as I have 

 ascertained by extracting them from the subthoracic pouch of the female) correct. 



Hence, by taking the preceding observations into consideration, we find that one 

 or more types of each of the great groups of the typical Malacostracous Crustacea 

 have been ascertained to undergo no change of form sufficiently marked to warrant 

 the employment of the term metamorphosis. Thus, 



^The Br achy ur a are represented by the Land Crab. 



The Macroura Cray-fish. 



The Schizopoda Mysis, 



The Amphipoda Gammarus and Phronyma. 



The Lcemodipoda Caprella and Cyamus. 



The Isopoda Asellus, Cymothoa, and Limnoria. 



Note. — Since the preceding pages were written, Mr. Thompson has published a 

 memoir upon the genus Pinnotheres, belonging to the Brachyura, in which the ova 

 are stated to have been seen to hatch in great numbers under the form of a new kind 

 of Zoe, without the circumstances attending their development being recorded. And, 

 on the other hand, some of the late Mr. Guilding's MSS. have been published in the 

 Magazine of Natural History, in which it is distinctly stated that the land Crabs do 

 not undergo transformations. 



