400 NATURAL SCIENCE. June, 



the comparatively prepotent, newly acquired, adaptive characters are 

 first manifested in the nepionic and neanic stages instead of in adults, 

 as in Amphibia. 



The Insecta of the more specialised orders, x.-xvi., afford, next 

 to some parasites, the most notable examples of this mode of 

 evolution. Their larval or nepionic, and pupal or neanic, stages are 

 prolonged at the expense of the ephebic, winged, stage, and the 

 reasons for this prolongation are found in the great number of new 

 features introduced into these stages of development in these orders 

 as contrasted with those of the more primitive and, in large part, 

 more ancient orders, i.-ix. The law of tachygenesis has been at 

 work here, as in the former cases alluded to above, and it is shown in 

 the encroachments of the adaptive characteristics of the caterpillar, 

 grub, and maggot upon the inherited characters of the Thysanuran 

 stage, which loses its ancestral characteristics, until in most cases 

 they are either obsolete or recognisable with difficulty. 



The habits and structures which have been evolved in different 

 types for continuing the life of the individual through the winter occur 

 only in animals likely to be injured or to perish if exposed without 

 some defence, and vary from the horny coverings of the winter buds 

 of fresh-water sponges, Bryozoa, and Crustacea, to the storage of 

 provisions in sheltered places by land-animals, and even hibernation 

 may perhaps be included under this head, since this is equally the 

 result of inability to lead an active life under the rigorous conditions 

 of extremes of temperature. 



The old view that the larval stage arose as an adaptation 

 acquired by the insect according to its surroundings, providing either 

 a caterpillar, grub, or maggot, and that these lead necessarily to a 

 more or less protracted quiescent pupa stage, in which the animal can 

 pass through the dangerous time without feeding, is more easily 

 supported than any other view. It is certainly more in accord with 

 obvious facts than the view that this stage arose because it was 

 essential to the good or success of the species in the struggle for 

 existence, or some other equally obscure teleological cause ; as, for 

 example, that each individual ought to have a prolonged period of 

 rest in which to elaborate its complex internal and external anatomy. 



As a matter of fact, we do not see how the same argument can 

 be applied to the Odonata or Orthoptera, whose structure is certainly 

 very complex, and which, in their insectal peculiarities, are not so far 

 behind the higher orders as to justify the assumption that their 

 differences of structure must necessarily be provided for by modes of 

 development that are so disproportionately complex. If this be met 

 by the assertion that their wings are transparent and their ephebic 

 organs materially simpler than those of the orders x.-xvi., how is it 

 that Ephemeroptera and Platyptera, which are very highly specialised 

 in the ephebic stage, have no quiescent stage which can be compared 

 with the pupa, and yet the Coccidae, among Hemiptera, have such 



