xiv PROOFS OF ORGANISING MIND 299 



on the anatomy, physiology, and development of which he 

 has published an elaborate work in two volumes dealing 

 with every part of the subject. He considers the two- 

 winged flies to be the highest development of the insect- 

 type ; and though they have not been so popular among 

 entomologists as the Coleoptera and Lepidoptera, he believes 

 them to be the most numerous in species of all the orders of 

 insects. I will now endeavour to state in the fewest words 

 possible the general results of his studies, as well as those of 

 the students of the other orders mentioned, which are all in 

 substantial agreement. 



In those insects which have the least complete meta- 

 morphosis the cockroaches the young emerge from the 

 egg with the same general form as the adult, but with 

 rudimentary wings, the perfect wings being acquired after a 

 succession of moults. These seem to be the oldest of all 

 insects, fossilised remains of a similar type being found in 

 the Silurian formation. Locusts and Hemiptera are a little 

 more advanced, and are less ancient geologically. Between 

 these and the four orders with complete metamorphosis 

 there is a great gap, which is not yet bridged over by fossil 

 forms. But from a minute study of the development of the 

 egg, which has been examined almost hour by hour from 

 the time of its fertilisation, the conclusion has been reached, 

 that the great difference we now see between the larva and 

 imago (or perfect insect) has been brought about by a 

 double process, simultaneously going on, of progression and 

 retrogression. Starting from a form somewhat resembling 

 the cockroach, but even lower in the scale of organisation, 

 the earlier stages of life have become more simplified, and 

 more adapted (in the case of Lepidoptera) for converting 

 living tissues of plants into animal protoplasm, thus laying 

 up a store of matter and energy for the development of the 

 perfect insect ; while the latter form has become so fully 

 developed as to be almost independent of food-supply, by 

 being ready to carry out the functions of reproduction 

 within a few days or even hours of its emergence from the 

 pupa case. 



At first this retrogression of the earliest stage of life 

 towards a simple feeding machine took place at the period 



