488 ORIGIN" OF SPECIES 



Afterwards they undergo a complete change; their eyes dis- 

 appear ; their legs and antennae become rudimentar\-, 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 development of the 

 new class would be widely different from that of our exist- 

 ing 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 embr\'onic 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 malacos- 

 traca, appear at first as larvse under the nauplius-form; and 

 as these larvae 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 Xauplius, existed, and subsequently produced, along sev- 

 eral divergent lines of descent, the above-named great Crus- 

 tacean 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 all within each class have, according to our theory, been 

 connected together by fine gradations, the best, and, if our 

 collections were nearly perfect, the only possible arrange- 

 ment, 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 under- 

 stand how it is that, in the eves of most naturalists, the 



