MUTUAL AFFINITIES OF ORGANIC BEINGS 395 



which they probably would have retained through inheritance, if 

 they had really been metamorphosed from true though extremely 

 simple legs, is in part explained. 



DEVELOPMENT AND EMBRYOLOGY 



This is one of the most important subjects in the whole round 

 of natural history. The metamorphoses of insects, with which 

 every one is familiar, are generally effected abruptly by a few 

 stages; but the transformations are in reality numerous and 

 gradual, though concealed. A certain ephemerous insect (Chloeon) 

 during its development moults, as shown by Sir J. Lubbock, above 

 twenty times, and each time undergoes a certain amount of 

 change; and in this case we see the act of metamorphosis per- 

 formed in a primary and gradual manner. Many insects, and espe- 

 cially certain crustaceans, show us what wonderful changes of 

 structure can be effected during development. Such changes, how- 

 ever, reach their acme in the so-called alternate generations of 

 some of the lower animals. It is, for instance, an astonishing fact 

 that a delicate branching coralline, studded with polypi, and at- 

 tached to a submarine rock, should produce, first by budding and 

 then by transverse division, a host of huge floating jelly-fishes; 

 and that these should produce eggs, from which are hatched 

 swimming animalcules, which attach themselves to rocks and be- 

 come developed into branching corallines ; and so on in an endless 

 cycle. The belief in the essential identity of the process of alternate 

 generation and of ordinary metamorphosis has been greatly 

 strengthened by Wagner's discovery of the larva or maggot of a 

 fly, namely the Cecidomyia, producing asexually other larvae, and 

 these others which finally are developed into mature males and 

 females, propagating their kind in the ordinary manner by eggs. 



It may be worth notice, that when Wagner's remarkable dis- 

 covery was first announced, I was asked how was it possible to 

 account for the larvae of this fly having acquired the power of 

 asexual reproduction. As long as the case remained unique, no an- 

 swer could be given. But already Grimm has shown that another 

 fly, a Chironomus, reproduces itself in nearly the same manner, 

 and he believes that this occurs frequently in the order. It is the 

 pupa, and not the larva, of the Chironomus which has this power; 

 and Grimm further shows that this case, to a certain extent, 

 ^'unites that of the Cecidomyia, with the parthenogenesis of the 

 Coccidae;" the term parthenogenesis implying that the mature 

 females of the Coccidae are capable of producing fertile eggs with- 

 out the concourse of the male. Certain animals belonging to sev- 



