THE METAMORPHOSES OF CRUSTACEA 67 



gotten or misunderstood till they were confirmed 

 by Mr. J. Vaughan Thompson, a naval surgeon 

 stationed at Cork, the first part of whose " Zoological 

 Researches " was published in 1828. Thompson's 

 statements were much disputed at the time, but they 

 have been confirmed by subsequent research, and it 

 is now known that the majority of Crustacea undergo 

 a more or less extensive metamorphosis after leaving 

 the egg, although, as will be seen later, there are 

 many important exceptions to this rule. 



If a fine muslin net be towed at the surface of the 

 sea on a calm day, and the contents turned out into 

 a jar of sea-water, it will usually be found to have 

 captured, among other things, clouds of animated 

 specks, which dance in the water or dart hither and 

 thither with great rapidity. Many of these specks, 

 when examined with the microscope, will be found 

 to be Crustacea. Besides adult animals belonging 

 to various groups, such as the Copepoda, which pass 

 the whole of their life swimming near the surface of 

 the sea, there will be numerous larval stages of species 

 which in their adult form live on the sea-bottom. 

 The identification of the species to which the various 

 larvae belong is a matter of considerable difficulty, 

 and, although the general course of development is 

 now well known for all the chief groups of Crustacea, 

 there are very many even of the common British 

 species in which the larval transformations have not 

 yet been worked out in detail. 



