Chap. XIV. Development and Embryology. 395 



with six legs, two long antennas, and four eyes. These larva? are 

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

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

 larva? spring on them, and afterwards crawl on to the females whilst 

 paired with the males. As soon as the female bee deposits her 

 eo-crs 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 

 antennas become rudimentary, and they feed on honey ; so that they 

 now more closely resemble the ordinary larva? 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 development of the new class would 

 he 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, entomostraca, and 

 even the malacostraca, appear at first as larva? under the nauplius- 

 form ; and as these larva? live and feed in the open sea, and are not 

 adapted for any peculiar habits of life, and from other reasons 

 assigned by Fritz Mtiller, it is probable that at some very remote 

 period an independent adult animal, resembling the Nauplius, 

 existed, and subsequently produced, along several divergent lines of 

 descent, the above-named great Crustacean groups. So again it is 

 probable, from what we know of the embryos of mammals, birds, 

 fishes, and reptiles, that these animals are the modified descendants 

 of some ancient progenitor, which was furnished in its adult state 

 with branchiae, a swim-bladder, four fin-like limbs, and a long tail, 

 all fitted for an aquatic life. 



As all the organic beings, extinct and recent, which have ever 

 lived, can be arranged within a few great classes ; and as ail within 

 each class have, according to our theory, been connected together 

 by fine gradations, the best, and, if our collections were nearly per- 

 fect, the only possible arrangement, would be genealogical ; descent 

 being the hidden bond of connexion which naturalists have been 

 seeking under the term of the Natural System. On this view we 

 can understand how it is that, in the eyes of most naturalists, the 

 structure of the embryo is even more important tor classification 





