74 INSECT TRANSFORMATION 



preceding chapter it has been seen that there is very little 

 divergence in the case of the grasshopper, and a somewhat 

 wide difference in that of the dragon-fly. Between these two 

 types a long series may be intercalated, while insects may be 

 found in which there is a wider divergence between imago and 

 larva than in the dragon-flies, and others in which the young 

 differs from its parent less than a young grasshopper does. The 

 aphids may fairly be claimed as examples of the latter. For 

 while the newly-hatched grasshopper is distinguished from the 

 adult by a characteristic relative shortening of the abdomen 

 as compared with the thorax, the newly-hatched or newborn 

 aphid is a closely approximate miniature of its parent, with 

 which it agrees in the general form and proportions of its 

 body. 



Reference has already been made to the modification of the 

 aphid's jaws for piercing and sucking, a character which it 

 shares with all the members of its order. Other features of 

 the head in these insects are the small but prominent compound 

 eyes and the feelers (Fig. 40 b d) of six or seven segments, 

 whereof the first and second are short and stout, while the 

 others are elongate and slender, the cuticle provided with ring- 

 like sense-organs ; the last segment of the feeler is suddenly 

 constricted not far from its base, its terminal portion tapering 

 and showing incomplete transverse furrows. In winged aphids 

 the mesothorax and metathorax are relatively broader than 

 in the wingless forms (Fig. 39 a c) and the tergal exoskeleton 

 well developed, as is necessary to give attachment to the 

 wing-muscles. In wingless forms, the thorax is hardly 

 differentiated from the abdomen, and the cuticle is generally 

 thin and soft all over the body. The abdomen is ovoid in 

 shape, broadest at its third or fourth segment and tapering to 

 the tail-end ; the sixth segment carries a pair of prominent 

 outstanding tubes, the cornicles, organs most characteristic of 

 the family, which pour out a sticky protective secretion. The 

 legs of an aphid are relatively long, and feebly spiny, the foot 

 consisting of two segments only. 



In the newly-born young the general form and proportions 

 of the adult are closely reproduced, 1 the legs and cornicles 



1 A. C. Baker and W. F. Turner : " Morphology and Biology of the 

 Green Apple Aphis ". Journ. Agric. Research, V. 1916. 



