DEVELOPMENT AND EMBRTOLOOT. 465 



mals. The adult might also become fitted for sites or 

 habits, in which organs of locomotion or of the senses, etc., 

 would be useless; and in this case the metamorphosis 

 would be retrograde. 



From the remarks just made we can see how by changes 

 of structure in the young, in conformity with changed 

 habits of life, together with inheritance at corresponding 

 ages, animals might come to pass through stages of devel- 

 opment, perfectly distinct from the primordial condition 

 of their adult progenitors. Most of our best authorities 

 are now convinced that the various larval and pupal stages 

 of insects have thus been acquired through adaptation, and 

 not through inheritance from some ancient form. The 

 curious case of Sitaris — a beetle which passes through cer- 

 tain 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 antennag, and four eyes. These larvee are 

 hatched in the nests of bees; and when the male bees 

 emerge from their buri-ows, in the spring, which they do 

 before the females, the larvs spring on them, and after- 

 ward crawl on to the females while paired with the males. 

 As soon as the female bee deposits her eggs on the surface 

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

 leap on the eggs and devour them. Afterward 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 larvse 

 of insects; ultimately they undergo a further transforma- 

 tion, 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 development of the new class 

 wonld 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 theprogenitor of the whole 

 group in its adult state. In the great class of the Crus- 

 tacea, forms wonderfully distinct from each other, namely, 

 suctorial parasites, cirripedes, entomostraca, and even the 



