IN THE DECAPODOUS CRUSTACEA. 361 



occasionally walks by means of its thoracic members, now become simple, but more 

 commonly swims by the motion of its subabdominal fins, which are greatly developed 

 for this purpose =»<=. In both stages it is therefore a Macroura, but only in the latter 

 evidently related to the Decapoda. 



It will be quite superfluous to enter into a minute detail of the structure of this 

 Megalope, further than may be collected by a reference to the figure and its accom- 

 panying explanation. 



It must certainly be considered surprising that so many curious facts should have 

 remained until the present time undiscovered ; but still more, that from the first 

 announcement of metamorphosis no person has attempted to follow it up ; so that I 

 have not only the honour of the discovery, but also the entire merit of having ren- 

 dered this interesting part of the natural history of the Crustacea nearly complete, 

 as the announcements in the previous part of this memoir testify, and my subsequent 

 memoirs will prove. 



The facts connected with the metamorphosis in the Crustacea and the Cirripedes 

 are indeed so much at variance with our previous knowledge, with the dicta of some 

 of our leading naturalists, and of so very extraordinary a nature, that the scepticism 

 which still exists with regard to them may admit of some excuse. The approaching 

 summer I hope will put it in my power to remove all doubts upon the subject, by 

 submitting such of them as offer themselves to the scrutiny of other observers, a cir- 

 cumstance which never occurred to me as necessary beyond the circle of my own 

 family ; had there been any zoologists in my neighbourhood the case would have 

 been different, but in respect of this branch of science I here unfortunately stand 

 alone. 



Whatever indifference may be charged to our own zoologists in regard to these 

 important discoveries, we must do our scientific neighbours the French the justice of 

 noting, that they immediately took up the subject, and two naturalists were selected 

 and deputed to spend a summer at Isle Re, to make their observations. However, 

 by a subsequent report of one of these gentlemen, M. Milne-Edwards, to the French 

 Institute, it appears that so far from verifying the metamorphosis in Crustacea, he 

 pronounced that they were hatched with the form and structure of their adult 

 parent ! The observations upon which this decision was based I have not seen 

 stated ; but whatever they may have been, they are completely invalidated by the 

 positive proofs I have given and enumerated in the present memoir. 



The animals of this class are so recondite in their habits, so difficult to preserve 

 alive for any time, so little known to naturalists beyond the more common species, 

 that the investigation is necessarily attended with great difficulty and frequent dis- 

 appointment. It must be allowed that I have been peculiarly fortunate ; and I am 

 so sensible of the obligation I owe to that Source from whence springs all our 



* Fig. 3. 

 3 a2 



