252 DEVELOPMENT AND EMBEYOLOGY. [Cuap. XIV. 



beetle whicli 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 

 antennse, and four eyes. These larvse 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 larvae 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 larv?e 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 

 ordinary larvae of insects ; ultimately they undergo a 

 further transformation, and finally emerge as the perfect 

 beetle. Now, 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 develop- 

 ment 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 

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

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



