Art. XXIV. — Memoir on the Metamorphosis in Porcellana 

 and Portunus. By J. V. Thompson, F. L. S., Deputy 

 Inspector-General of Hospitals. 



Metamorphosis in Porcellana. 



Perceiving in the May Number of the Magazine of Na- 

 tural History, that doubts are still entertained by naturalists, 

 not only of the universality of metamorphosis in the Crustacea, 

 but more especially in regard to certain species and genera, 

 I am particularly happy to have it in my power to satisfy the 

 doubts of one gentleman, Mr. Westwood, {loc. cit.) with regard 

 to Porcellana, which, for particular reasons, he appears to 

 think must form one exception. 



It is well known to Crustaceologists that this anomalous 

 genus constitutes the connecting link between the Brachyura 

 or crabs, and the Macroura; having the extensile tail of the 

 latter, the body of the former, and a kind of intermediate form 

 of all the other parts, and admirably illustrates that axiom of 

 Linnaeus — " Natura non facit saltus" When, therefore, the 

 extraordinary facts relating to the metamorphosis of the 

 Brachyura and Macroura had become known to me, I 

 naturally felt a great desire to ascertain whether the same law 

 prevailed with regard to this intermediate genus, and was so 

 fortunate as to succeed in hatching the spawn of the species of 

 Porcellana, which we have in such abundance in the deep 

 water of the harbour of Cove. I had previously discovered, 

 by towing, a very remarkable Zo'e, totally different in aspect 

 from all those known or described. This was on the 28th of 

 May ; and what is very singular, in four days after, viz. the 

 2d of June, I had the high gratification of seeing the very same 

 Zot emanate from the ripe spawn of Porcellana, (fig. 1.) 

 Notwithstanding the minuteness of this curious larva, it is 

 rendered conspicuous against the light, by reason of its very 

 long spines, and may be taken in great abundance during the 

 whole of the month of June. 



In this instance we have another proof, in addition to that 

 of Pinnotheres, given in the present volume, p. 85, that the 

 Zoea, or larvae of the Crustacea, differ materially in the length 

 and disposition of the spines and form of tail. In the present 



