252 DEVELOPMENT AND EMBRYOLOGY. [Chap. XIV. 



beetle which passes through certain unusual stages of 

 development — will illustrate how this might occur. The 

 first larval form is described by M. Fabre, as an active, 

 minute insect, furnished with six legs, two long anten- 

 nae, and four eyes. These larvae are hatched in the 

 nests of bees; and when the male-bees- emerge from 

 their burrows, in the spring, which they do before the 

 females, the larvas spring on them, and afterwards crawl 

 on to the females whilst paired with the males. As 

 soon as the female bee deposits her eggs on the surface 

 of the honey stored in the cells, the larvae of the Sitaris 

 leap on the eggs and devour them. Afterwards they 

 undergo a complete change; their eyes disappear; their 

 legs and antennae become rudimentary, and they feed on 

 honey; so that they now more closely resemble the ordi- 

 nary larvffi of insects; ultimately they undergo a further 

 transformation, and finally emerge as the perfect beetle. 

 N'ow, if an insect, undergoing transformations like those 

 of the Sitaris, were to become the progenitor of a whole 

 new class of insects, the course of development of the 

 new class would be widely different from that of our 

 existing insects; and the first larval stage certainly 

 would not represent the former condition of any adult 

 and ancient form. 



On the other hand it is highly probable that with 

 many animals the embryonic or larval stages show us, 

 more or less completely, the condition of the progenitor 

 of the whole group in its adult state. In the great class 

 of the Crustacea, forms wonderfully distinct from each 

 other, namely, suctorial parasites, cirripedes, entomo- 

 straca, and even the malacostraca, appear at first as 

 larvffi under the nauplius-form; and as these larvae live 

 and feed in the open sea, and are not adapted for any 



