2 MEMOIR I. 



One of the objects therefore of tlie present Memoir, 

 will be to show the erroneous nature of this opinion, and 

 to announce the important discovery, that the greater 

 number of the Crustacea do actually undergo transforma- 

 tions, of which, in addition to the facts now adduced^ 

 further instances will be given in future memoirs. 



The circumstance of the Crustacea being supposed to 

 pass through no intermediate form, has been brought 

 forward heretofore as one of the arguments for their sepa- 

 ration from Insects ; but, although the fallacy of that 

 opinion may diminish the number of the characteristics 

 which distinguish these two tribes of animals as distinct 

 Classes, there yet remains those depending on the anato- 

 mical structure of their respiratory and circulating systems, 

 which are (|uitc sutficient to render the separation perma- 

 nent. It may also be observed, that the changes presented 

 to our notice in the Crustacea are quite peculiar, and of 

 a totally ditfercnt description from those of Insects. 



The sea (which is the habitation of the greater part of 

 the Crustacea,) to the casual observer, offers nothing but 

 an immense body of water, liere and there presenting a 

 solitary whale, or a vagrant troop of some of the smaller 

 Cetaceous animals; the appearance of a fish of almost any 

 other kind in the track of a vessel over the vast expanse 

 of the open ocean, is regarded even by the mariner, as a 

 kind of phenomenon, and creates an interest not to be 

 appreciated by those who have not engaged in distant 

 voyages. The fathomless parts of the ocean certainly do 

 not offer the same profusion of inhabitants with the shores 

 of Islands and Continents, or those parts where the 

 bottom is within the reach of the sounding line, or where 

 its surface is interspersed with fields of Sargosa (Fuciis 

 natans ;) on due examination however, we shall not fail 

 to find it every where peopled by a considerable variety of 

 animals either of small size, or possessed of such a degree 

 of translucency as to render them invisible, or scarcely 



