ON THE BRACHYUROUS DECAPOD CRUSTACEA. 



BROUGHT FROM THE CAPE BY DR. SMITH. 



The most interesting obsei"vations on Crustaceous animals which have of late years been 

 given to the public are those of Dr. Vaughan Thompson, relating to their metamorphosis. 

 It had been long recorded that many Entomostraca undergo metamorphosis ; but no naturalist 

 before Thompson ever ventured to affirm that crabs, lobsters, and the higher Crustacea 

 generally, pass through certain changes of form after leaving the egg. It is true, that in conse- 

 quence of the publications of Professor Rathke, some persons disputed the truth of Dr. 

 Thompson's assertions ; but so far as my own observations allowed me to form an opinion on 

 the subject, I was ever inclined to think that this gentleman merited well of science, which is far 

 more than could be said of any of those persons who by crude inferences, but never by direct obser- 

 vation, ventured to attack him.* I have never myself lived sufficiently near the sea-side 

 to enable me conveniently to repeat Dr. Thompson's experiments ; but looking merely to what 

 I have seen with my own eyes, I think it will eventually be found that the Ptilota of Aristotle 

 may be characterized by their change of form taking place during their last two or three stages 

 of ecdysis ; while the metamorphosis of all other Annulosa only occurs during the first or 

 second moult after leaving the egg. When I come to treat of the Macrourous Decapods, I 

 shall return to this subject. At present my attention must be more particularly confined to 

 the classification of the Brachyura, as being the best known groupe of all Crustacea. 



M. Latreille and Dr. Leach left systems behind them for the arrangement of Crustacea^ 

 which were professedly artificial, although the former naturalist made several praiseworthy 

 attempts to arrange these animals naturally. Since the death of these eminent naturalists, two 

 authors have appeared with higher pretensions to acquaintance with the class. The first of 

 these, M. Milne Edwards, having previously made some ingenious observations on the 

 economy and internal anatomy of Crustacea, has lately, in the " Suites de Buffon," produced 

 a classification, of which I can only say, that it makes an approach to be a rare exception to 

 the well-known fact, that professed comparative anatomists are the persons, of all others, who 

 in general are the most incapable of using their own observations for purposes of natural 

 arrangement. And indeed this very arrangement of Edwards is not natural, since he unfortu- 

 nately conceives that every groupe he can invent, provided he can furnish it with a character, 

 must be therefore a good one. As, on the contrary, the true definition of a complete natural 

 groupe is, that it must be a series returning into itself, many of the groupes of Milne Edwards, 

 when weighed by this scale, will be found wanting. For instance, of his four grand groupes, 

 Oxyrhynques, Cyclometopes, Catometopes, and Oxystomes, perhaps only his Cyclometopes form a 



* The credit of confirming Thompson's observations belongs to my friend Captain Ducane, R. N., who has made at 

 Southampton most interesting observations on the Metamorphosis of Crustacea, which I trust he will soon give to the Public. 



