IN THE ANIMAL KINGDOM. 103 



than in the case of Insects, owing partly to the real magni- 

 tude of the changes which take place, and partly also to the 

 prominence with which they are brought under the eye of 

 the observer. 'The embryo even of Mammalia undergoes 

 in the course of its development a series of remarkable 

 changes, very parallel to the metamorphosis of an insect ; 

 the conformation of its vascular system, for instance, is 

 changed more than once, and certain provisional organs, 

 such as the wolffian bodies, the umbilical vesicle, and the 

 allantois, appear, which are afterwards absorbed or cast off. 

 But these transformations have only been traced by labo- 

 rious anatomical investigations, as they are all gone through 

 in the interior of the uterine cavity in those hidden re- 

 cesses where the new being is " made secretly, and fashioned 

 beneath in the earth," as it were while in the Insects and 

 some others of the lower animals, the embryo being ex- 

 truded, not only from the body of the parent, but also from 

 its own egg-coverings, while still in an unformed or larva 

 state, the whole subsequent course of metamorphosis takes 

 place in the outer world, and is in great measure presented 

 naked to our view. Larvse are not unknown in other 

 forms of animal life even among Vertebrata they occur in 

 the case of the Batrachia and Marsupialia, and also in some 

 Fishes* but in Insects they are not the exception but the 

 rule the guise under which the young are normally 

 brought forth. 



Entomologists distinguish three stages in the develop- 

 ment of Insects, by the terms larva, pupa, and imago. 

 But these expressions do not always indicate homologous 

 conditions, for the point of development at which the young- 

 quits the egg varies considerably in different orders of the 

 class. "In all cases the germinal mass, while still within the 



* The metamorphosis is very marked in the Lamprey. Miiller's 

 Archives Anat. Physiol. (1856), p. 323. 



