INSECTS INJUEIOUS TO CONIFERiE. 



171 



they also are wingless, oval, of small shape, and of a purplish- 

 black colour, and have a long bristle-like sucker with which they 

 penetrate the needles to feed on their sap. Towards the end of 

 April they lay forty to fifty eggs on the twigs. The young pro- 

 duced scatter themselves over the needles, and do not live 

 enclosed in a gall ; at first very minute and blackish, they grow 

 rapidly and become covered with a whitisli woolly down exuding 

 from pores on their body, giving the trees the appearance of being 

 covered with minute scattered snow-crystals. About June they 

 acquire wings and spread the species, while further broods are 

 produced till the autumn. This insect occurs on Larches of 

 all ages, being found, perhaps, most frequently on trees of 

 ten to twenty years old ; it not seldom affects young Larches in 

 nurseries, and may there be very troublesome. 



The facts thus briefly given about the two kinds of Chermes 

 are those which are commonly known and recorded. It will be 

 seen that nothing is said about the presence of any male forms 

 or of a sexual generation ; and, indeed, till recently nothing was 

 accurately known about the existence of the male. In 1883 Mr. 

 Buckton detected the very minute wingless male of C. Abietis in 

 England, and somewhat later the series of papers by German 

 observers already referred to have thrown much light on the life- 

 history of these insects. It may be taken as proved by them that 

 Chermes Abietis and Laricis are different forms of one and the 

 same species which migrates between two food-plants, certain 

 stages in the life-cycle being passed on the Spruce, certain stages 

 on the Larch. Such instances where the full cycle of forms is 

 not completed in one generation are not unknown amongst other 

 insects, especially among the Ai^hides, while the Phylloxera, 

 nearly allied to Chermes, supplies us with a familiar and striking 

 case. Similar examples are furnished by other parasitic 

 animals and plants, notably the tapeworms and liver-flukes, and 

 the Fuccinias {^cidiomycetes) among fungi. These life-cycles 

 are usually associated, as in the instances referred to, with a 

 change of host, or, as in the Phylloxera of the Vine, with change 

 of situation on the same host ; that is, certain generations in the 

 life-cycle are always passed on or in one host, other generations 

 on another host, and it is commonly found among insects that 

 the complete cycle comprises one sexually produced genera- 

 tion, which may be said to start the cycle, and numerous 



