THE OPEN TYPE OF WING-GROWTH 91 



as a protective hood or ovisac. In rare instances the male 

 as well as the female is wingless, and it is of great interest to 

 find in such a case (the species Apterococcus fraxini for example) 

 that the resting " pupa ", so characteristically associated with 

 wing-growth, occurs as the penultimate stage of the life-history 

 although wings are never developed in either sex. 



There is yet another order of insects, illustrating the open 

 type of wing-growth, to which reference may now be suitably 

 made, as they exhibit not a few features that throw light on 

 some of the larger problems raised by a study of insect trans- 

 formations. These are the mayflies (Ephemeroptera), 1 



FIG. 50. MEALY-BUG (PseudoCOCCUS 



a, larva (dorsal view) |; b, female (ventral view), x a, 45 ; 



b, 20. After Carpenter, Econ. Proc, R. Dublin Soc. II. 



creatures whose life-history involves, like that of the dragon- 

 flies described in the preceding chapter, a transition from water 

 to air, though they offer in many respects a striking contrast 

 to the latter group. Mayflies (Fig. 51 A) are delicate, fragile 

 insects with the jaws so excessively reduced that they are 

 unable to feed, differing thus as widely as possible from the 

 dragon-flies, those voracious hunters of the air. A mayfly's 

 compound eyes are large and prominent, each eye divided, in 

 some males, into two regions, the inner of which crowns an 

 outstanding, pillar-like prominence of the head ; there are 

 also three simple eyes (ocelli). The feeler is short, consisting 



1 A. E. Eaton : "A Revisional Monograph of Existing Ephemericte or 

 Mayflies ". Trans. Linn. Soc. (Zoo/.) (i), III. 1882-5. L. C. Miall : " The 

 Natural History of Aquatic Insects ". London, 1895. 



