OF WASHINGTON. 121 



though here we have experimental evidence of remarkable life 

 persistency under abnornal conditions, as I have known a speci 

 men of A.rg'as reflexus to remain alive in a corked vial without 

 food for some five years, moulting repeatedly during the period. 

 So with the Mites they have developed a most remarkable 

 adaptability to environmental requirements, the parasitic and 

 gall-making forms exhibiting long resting periods alternating 

 with periods of rapid multiplication ; while some of the soft- 

 bodied, non-parasitic forms are able to assume a Hypopus pro 

 tecting mail which permits a long period of quiescence until cir 

 cumstances again favor activity and reproduction. 



RETARDATION IN DEVELOPMENT. 



The subject of retardation in individual development is inti 

 mately bound up with the question of longevity. The annals of 

 entomological literatare are replete with instances of such retarda 

 tion, and, in this connection, I will content myself with a refer 

 ence to some of the more common instances, especially to those 

 that have come under my own personal observation. In the egg 

 state the instances of retardation of development, under normal 

 conditions, are few, as the period passed in the egg and the time 

 of hatching are very uniformly and regularly controlled by me 

 teorological and physical conditions, especially that of tempera 

 ture. Where eggs are laid in summer or autumn by monogo- 

 neutic species, there is sometimes shown a tendency to hatch the 

 same year, and thus produce a second annual generation, and 

 the converse of this is true, and such facts are more particularly 

 noticeable in species like the semi-domestic Sericaria mori, in 

 which the number of generations has been influenced by man 

 and has not become fixed through long periods of natural propa 

 gation. Yet, when the natural conditions are in any way inter 

 fered with, the almost unlooked-for pow r er of adaptation is well 

 illustrated by the somewhat exceptional case of the eggs of 

 Caloptenus spretus to which I have drawn attention in several 

 publications, especially in 1881 (Amer. Nat., iSSi, pp. 1007- 

 1008), where it is shown that eggs of this insect which were 

 laid in the autumn of 1876 and covered by a layer of clay and a 

 plank sidewalk, thus precluding the issuance of the young, re 

 mained latent four years longer than they normally would have 

 done, freely hatching during the spring of 1881, when the side 

 walk was taken up and removed. 



Retardation in the larva state is rarely witnessed among leaf- 

 feeding forms, though even here there will be great variation in 

 the relative time of development of the individuals of a given 



