AND THE LOWER ANIMALS. 97 



Among the other crustacean orders, and especially 

 among Entomostraca, we find an immense number of 

 species which undergo more or less complete meta- 

 morphoses. There is still much work to be done in 

 the great field opened by Ducasse and Thompson ; 

 but even now we may confidently assert that the 

 species of Crustacea which assume the perfect form 

 on emerging from the egg are probably in the 

 minority. It would be idle and indeed impossible to 

 enter into further details without the assistance of 

 numerous engravings. Besides, we should really be 

 travelling on ground we have already gone over; we 

 should only find what we have already observed; viz. 

 the creation of new structures, and the destruction, 

 modification, and increase of others. We find almost 

 invariably, that the final result of metamorphosis is 

 the progressive completion and elevation of the 

 organism. 



We see quite an opposite state of things in two 

 very curious secondary groups of this class Crustacea. 

 Here, to judge from appearances, metamorphosis 

 degrades the creature instead of elevating it, and 

 modifies the organism in such an unusual manner 

 that one is puzzled to know whether the animal is not 

 an abnormal one. Cuvier died in the belief that the 

 Balasnidse and Anatifera were mollusks, and that the 

 Lerneae were intestinal worms. 



It was Messrs. Thompson and Nordmann who first 

 corrected this double error. The former discovered 

 the true nature of the Cirrhipedia,* the latter that of 



* " Zoological Eesearches and Illustrations ; or, Natural History 

 of Nondescript or imperfectly-known Animals/' 1831. 



H 



