122 ENTOMOLOGICAL SOCIETY 



brood, and where the species is polygoneutic I have not infre 

 quently noticed that certain individuals of the spring brood would 

 beget one further generation during the year, while others would 

 beget two. In some instances, also, especially where there is 

 summer or autumn dormancy (Phyciodes, Apatura, etc.), a cer 

 tain portion of a brood will be retarded and go over till the en 

 suing year, while the balance will develop and transform the 

 same year. It is, however, among the larvas which live beyond 

 the growing season of the year, as in most of the species of wood- 

 and stem-boring and root-feeding Lepidoptera and Coleoptera, 

 as also those which feed on dead and dry animal or vegetal mat 

 ter, as shown in considering the Coleoptera, that cases of accel 

 eration and more particularly of retardation have been observed. 



The Heteroptera and Homoptera, the Mallophaga, the Spiders 

 and the Ticks, also show, as we have already seen, a remarkable 

 tendency to retardation, especially in the adolescent stages. 



In the pupa state there is less opportunity or occasion for devi 

 ation from the normal habit of the species, and yet the literature 

 of Lepidopterology furnishes more particularly very many in 

 stances of belated pupal development, or of instances where an 

 individual in a given brood has passed on to a second or third 

 year in the cocoon, while other individuals have developed and 

 given out the imago at the normal period. This has happened 

 frequently in my own rearings of insects, and particularly in the 

 Bombycida3, and there are innumerable recorded cases by others. 



In the imago state the cases of retardation are numerous, but 

 almost always in connection with abnormal conditions. Thus, 

 as we have seen, they chiefly refer to hard-shelled insects like 

 beetles, which have been kept in confinement without food and 

 measurably protected from the influence of the weather. The 

 most marked cases of this kind are of wood-boring beetles, es 

 pecially Longicorns and Ptinidse, which are known to have 

 existed alive in wood very many years after the wood had been 

 made up into household furniture. 



INFLUENCE OF PROLONGED COLD ON RETARDATION. 



Just how long the dormant state in insects, especially in the 

 pupa state, could be extended by continuous cold, it would be 

 difficult to tell ; but experiments have been made, especially by 

 Mr. William H. Edwards, in this country, which indicate not 

 only that this state may be very materially prolonged beyond 

 the normal period, but that the results of such prolongation 

 almost justify the belief that, in those species which withstand 

 extremely low temperatures which, to use a common expres- 



