332 Experimental Zoology 



history, as shown by Blochmann, Dreyfus, and others. The 

 young appear in the spring on the fir. They become mature 

 and deposit eggs. The young developing from these eggs pro- 

 duce galls, within which they mature as winged individuals. 

 Most of these leave the fir and go to the larch, where each female 

 deposits about 40 eggs, which, hatching in 10 to 14 days, pro- 

 duce young that feed on the leaves. Later these wander to the 

 stem, where they hide in the crevices throughout the winter. In 

 the spring they grow larger and begin to lay eggs about the 

 middle of April. The eggs soon hatch and the young wander up- 

 ward to the young needles, on which they feed and grow to winged 

 parthenogenetic females. These leave the larch about the end 

 of May and fly to the fir, settling down on the under sides of 

 the old leaves, where they deposit 8 to 10 stalked eggs from which 

 sexual males and females develop. These pair and the female 

 lays one egg on the stem. The eggs develop slowly, the young 

 emerging in October. They wander to the bases of the buds, 

 stick the proboscis into them, and winter in this condition. In 

 the spring the female deposits many eggs, from which the young 

 that emerge are those that produce the galls first mentioned. 

 This brings the cycle back to the starting point. 



There is also in Chermes what is known as a parallel or col- 

 lateral series. Part of the parthenogenetic females on the fir 

 that are late in leaving the galls remain on the fir, and deposit their 

 eggs there (instead of on the larch). The young wander to the 

 ends of the branches, where they remain until the next spring with 

 the proboscis stuck into the tissues of the buds. In the spring 

 they produce galls. Presumably the cycle may begin again from 

 the individuals that emerge from these galls, which have, as it 

 were, short-circuited the life-cycle. 



It is of great interest to observe that the sexual forms do not 

 appear in this short-circuited generation that remains on the fir, 

 and the inference is plausible that the conditions existing on the 

 larch are those that call forth the sexual forms. 

 In another species, the phylloxera of the grape, the alterna- 

 tion of generations takes place between the roots and the leaves. 



