4148 Notices of New Books. 



who, dissatisfied with the uncertainty and contradiction of former 

 testimony, resolved to investigate the matter for himself; and this he 

 effected with a degree of acumen and perseverance which character- 

 ize all his researches, and by which the truth of the doctrine is fully 

 established, as regards the genera Cancer, Zantho, Pilumnus, Carci- 

 nus, Portimus, Polybius, Maia, Galathea, Homarus, and Palinurus, — 

 a goodly number to have been investigated by one observer, — and of 

 some of these he watched every change. These results were pub- 

 lished in two Memoirs, read to the Cornwall Polytechnic Society in 

 1843; in which the author takes a clear and fair view of the whole 

 subject, and comes to his decision with a host of evidence sufficient 

 to set the substantive question entirely at rest. Unfortunately, the 

 useful local publication in which these Memoirs appeared, is so much 

 confined in its circulation, that it has probably fallen into the hands 

 of but few naturalists. 



" I have felt it desirable to give a more extended history of the dis- 

 covery, as, with the exception of Mr. R. Couch's first Memoir just 

 referred to, no such digest has ever been placed at one view before the 

 world. I now proceed to examine the actual results, and to endea- 

 vour to reduce the facts already known to some order. 



" It will be inferred from the previous account, that there are consi- 

 derable variations in the character of the metamorphosis of different 

 families, and that in the case of Astacus fluviatilis, there appears 

 at present to exist even an abrupt and isolated exception to the 

 general law. As this is the only case at present in which such 

 exception has been established, I refer my readers for further infor- 

 mation on this subject, to the work of Mr. Rathke himself, which 

 constitutes one of the most complete and elaborate monographs in 

 existence, illustrated in the most beautiful and perfect manner ; and 

 to the full and satisfactory analysis of the work by Milne-Edwards, 

 in the first volume of his ' History of the Crustacea.' 



" Eliminating, therefore, this exceptional case, it will be found that 

 the fact of a metamorphosis has been demonstrated with more or less 

 success in no less than seventeen genera of the brachyurous order of 

 the Decapoda — in which order the phenomenon is most decided and 

 obvious — belonging to the families Leptopodiadae, Maiadae, Cancer- 

 idac, Portunidae, Pinnotheridae, Grapsidae, and Gecarcinidae. In the 

 Anomourous order, it has been shown in the genera Pagurus, Porcel- 

 lana, and Galathea, and amongst the Macroura in Homarus, Palinu- 

 rus, PalaeiDon, and Crangon." — Introduction, p. xxxviii. 



