GENERAL REMARKS. 283 



apod form may be evolved in the adult stage. The 

 pupa is always a six-legged form, with the legs more 

 or less developed, and being common to all insects, 

 whether quiescent or active, is really a part of the 

 direct mode of development wherever it occurs. It 

 is as universal and essential as are the typical ovarian 

 and adult stages. Indirect development is, therefore, 

 composite. It is first a deviation in the larva from 

 the direct mode, and then a return in the pupa of 

 the direct mode, and this return necessarily brings 

 the organism back again into the normal line of evo- 

 lutionary changes, and the normal form of insect is 

 the result of this return and the resumption of pro- 

 gressive specialization. 



The reverse of this process, i.e. when direct develop- 

 ment is not resumed, is shown in the case of parasites 

 like the female of Stylops. 



If it be true that the stages of development in indi- 

 viduals are abbreviated records of the modifications 

 undergone by the group during its evolution in time, 

 and that as a rule the characteristics of adults of the 

 more generalized or primitive forms of any order, or 

 even of smaller divisions, in all groups of the animal 

 kingdom, show a tendency to occur in the young of 

 more specialized forms of the same group or division, 

 it follows, that in each natural group the speciahzed 

 forms have been evolved from the generalized forms. 

 This tendency to accelerate and abbreviate the record 

 preserved by heredity in the growth and development 

 of each individual can be understood if one imagines 

 a series of forms evolving in time. First, the repre- 

 sentatives of the simple, primitive ancestor; then 



