THE METAMORPHOSIS. 423 



earlier forms of the Artkrozoa, which have remained stationary upon a 

 lower grade, and, at a certain period of their lives, furnishes them with 

 merely pedal warts, then with hooked, short feet, then with branchiae 

 and natatory laminae, and, later, in their pupa state, with rudimentary 

 wings, and, lastly, with perfectly developed wings. Thus I conceive 

 to be explained the necessity of both the chief groups among insects. 



In insects with an imperfect metamorphosis there cannot, conse- 

 quently, be a passage through the earlier forms and grades of the 

 animal kingdom ; even the analogy which I formerly thought I detected 

 between them and the consecutive classes of the Gastrozoa, appears to 

 me now, upon a closer investigation, to be a merely playful endeavour 

 to discover resemblances, and which I consequently no longer value. 

 What I formerly, as a proof of such a repetition, deduced from the 

 successive development of the sexual organs, may, with equal justice, 

 be applied to all insects, or to all Arthrosoa, and, indeed, to all animals 

 whatsoever, in as far as in all, the perfecting of the genitalia progresses 

 with the gradual development of the creature. 



Nevertheless, all insects, notwithstanding this difference from each 

 other, must be recognised as members of the same class, and, indeed, 

 by reason of the uniformity of the figure of the whole body, that is, by 

 its division into three chief parts. This division of the body, which, 

 among all the Arthrozoa, is peculiar to insects alone, is their second 

 most important truly physiological character, which proves the equali- 

 sation of the contention between the various organs of the body, and in 

 the limitation of each individual organ to a particular and impassable 

 sphere of action, most clearly illustrates the fixed laws of its type of 

 structure, which is always a predominant character of highly developed 

 and perfected groups. The same law exhibits itself in the structure 

 of the mouth, the antennas, the wings, and, especially, in the number 

 and articulation of the legs, whence their number, restricted to six, 

 has always been considered as the safest character of insects. 



252. 



Having thus explained the significance of the insect metamorphoses, 

 it still remains for us to define distinctly the several changes which the 

 insect undergoes during these stages. Indeed, in the anatomical descrip- 

 tion of the organs of digestion and generation, we have already spoken 

 of the changes they experience during the metamorphosis (114 and 

 153) ; but these, changes have not yet been brought into connexion 



