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THE BOOK OF NATURE STUDY 



cut projection, the cremaster, whose minute spines are used for 

 attachment to the silken platform when the larval claspers are 

 cast off ; it represents the flap covering the anus of the larva. 

 The possession of mouth parts, legs and wings by an animal at 

 a time when it neither takes food nor moves from one place is 

 cause for surprise. The probable explanation of the phenomenon 

 is that at some remote period the pupa was not inert and stationary, 

 but active and capable of using all these organs. There are 

 many insects, e.g. grasshoppers, cockroaches, etc., which go 

 through no pupa stage, but reach the adult condition by a series 

 of gradual changes accomplished at each moult, and in these 

 the young as they leave the egg are not caterpillars, but in general 

 bodily form resemble the adult, except for the absence of wings. 

 Such insects have no " metamorphosis." Then, again, the 

 dragon flies possess an active pupa which exhibits no very marked 

 differences from the larva, but on leaving the water this pupa 

 gives origin to the perfect insect by a single abrupt change 

 accomplished at one moult. This state of affairs is known as 

 " partial metamorphosis," there being only one sudden change 

 of form ; whereas in the lepidoptera the metamorphosis is " com- 

 plete " with the two sudden changes, the first when the larva 

 turns to the pupa, the second when the pupa to the imago. 



Moreover, there is reason to suspect that at some period 

 the present lepidopterous pupa was the final form, and that the 



imago, as we now see it, 

 is a later development; 

 for the pupae possess ex- 

 ternal organs of reproduc- 

 tion differing in the two 

 sexes, so that it is possible 

 to distinguish male from 

 female chrysalids. These 

 external sexual differences 

 are to be looked for on the 

 ventral side of the eighth 

 and ninth abdominal segments. If the pupa be a male there is on 

 the gth segment ventrally a fine longitudinal groove in the middle 

 line on a slightly raised area and provided with two oval lips on the 



FIG. 68. Terminal segments of male (left) and 

 female (right) pupae. $, male organ ; $, female 

 organ ; a/, anal furrow. The numbers are 

 those of the segments. 



