262 THE ORIGIN OF SPECIES 



come rudimentary, and they feed on honey; so that they 

 now more closely resemble the ordinary larvae of iasects; 

 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 be 

 widely difierent 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, cirripeds, entomostraca, 

 and even the malacostraca, appear at first as larvss under 

 the nauplius-form; and as these larvse live and feed 

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

 habits of life, and from other reasons assigned by Fritz 

 Miiller, it is probable that at some very remote period 

 an independent adult animal, resembling the Nauplius, 

 existed, and subsequently produced, along several diver- 

 gent 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 swimbladder, four finlike 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 



