42 PREDACIOUS AND PARASITIC 



with less certainty in Agrion, Hemerobius, and other genera. In 

 Fig. 5 of the same plate is shown the wing of Agrion, which, while 

 remarkable for the rectangular shape of its cellules, presents in 

 some portions, and particularly in the irregular-shaped cellules 

 towards the lower margin, a distinct approach to the venation of 

 Chrysopa, which has been given in previous figures. But a more 

 curious feature is the manner in which the spaces between the 

 longitudinal nervures are divided at the extremity of the wing, 

 showing a relationship with the Trichoptera, in which such an 

 arrangement is a distinctive feature and of a noticeable character. 



The presence of the numerous fine short hairs upon the wing- 

 veins of Agrioji is also an indication of the affinity between this 

 genus and the Hemerobiidce. and Trichoptera, in the latter of which 

 the presence (in greater number) of similar short hairs upon the 

 wings has given rise to the subordinal designation. 



In concluding my remarks upon the wing structure, I would 

 advise the student to examine for himself the various wings under 

 a low-power objective, and to note the remarkable visual resem- 

 blance which is to be seen throughout the whole order — a resem- 

 blance which can be better realised by sight than by any amount 

 of description or even of figures. 



The last point which I shall consider is one on which much 

 stress has been laid by some writers, but as to the value of which 

 I feel considerable doubt in the present state of our knowledge. 

 No doubt the evidence afforded by embryology has been of great 

 value to biology and to comparative anatomy ; but the difficulties 

 which beset its practical application in the study of insects, are a 

 serious obstacle to forming conclusions of definite value, based on 

 such research alone. The embryological development of the genus 

 Calepteryx has been exhaustively studied by Brandt, whose 

 results are to be found in the Memoirs of the Imperial Academy of 

 Science at St. Petersburg, and in the German work which he has 

 published on the subject. With a view to compare the develop- 

 ment of this genus of the Odonata with the same developments in 

 one of the Flatinipennia, I have studied the egg-development in 

 Chrysopa, and have found it in the main to correspond with the 

 account given by Brandt, though important differences appear as 

 to the position of the embryo, both in relation to the egg itself 

 and to the yolk-mass. * 



