595 



further during the summer, but creep into cracks of the bark and remain 

 there until they moult next spring and become false stem-mothers. 

 The sexuparae and exules were previously mistaken for separate 

 species : C. laricis, Ratz., and G. haemadryas, Koch. The sexuparae 

 fly back to fir trees, where they deposit from 5 to 10 eggs on the lower 

 side of old branches ; the eggs are of two kinds : yellowish green eggSj 

 which produce male larvae in about two weeks, and reddish eggs, 

 which give rise to the female larvae. The females lay fertilised eggs 

 underneath the scales of the bark, from which the wintering stem- 

 mothers arise at the end of summer or in autumn. The exules oviposit 

 and produce larvae the structure of the skin of which is similar to 

 that of the hibernating larvae of false stem-mothers, and these suck 

 the needles of larches ; according to Borner, the descendants of the 

 exules are divided into hiemales and aestivales, but the author has 

 only found those corresponding with hiemales ; these larvae form a 

 second generation of exules. It has not been established how many 

 generations of them occur during one summer, their number evidently 

 depending upon the weather and temperature, but in any case it is 

 not less than two. The larvae from eggs laid by the last generation 

 of exules during the summer, hibernate and appear in spring as false 

 stem-mothers, their descendants being again divided into sexuparae 

 and exules. It is supposed that the exules compensate for the wastage 

 caused during the migration back to firs, when many sexuparae perish. 

 It is not known how long the multiplication of exules can go on without 

 the introduction of forms produced by new winged migrants from galls, 

 but apparently it has no fixed limits. Generally speaking, in the 

 absence of such new introductions, the number of sexuparae decreases 

 and only exules remain eventually. The cycle of this species is possibly 

 still more complicated and it may form both early and late variations. 

 The author has sometimes found in July, when the normal migration 

 of the winged forms has ended, oviparous winged forms on the bark 

 of larches, which, in contrast to the winged migrants of June, covered 

 their eggs with white down ; the larvae from such eggs were somewhat 

 different from the usual fundatrix spuria. The author calls this late 

 variety C. strohilohins var. tmdoides, but further researches are required 

 to show whether this variety is connected with the cycle of develop- 

 ment of C. strobilobius, or whether it is independent and constitutes 

 a self-contained cycle. 



Chermes lajjponicus, Choi., stands in the same relation to 

 C. strobilobius, as C abietis does to C. viridis. It forms exactly the 

 same galls, but has no migrations to larches and its multiplication is 

 exclusively parthenogenetic ; it is accordingly widely spread in the 

 fir woods of North Europe, where no larches are present ; it has only 

 two stages a year (stem-mothers and winged forms) and a one-yearly 

 cycle. The galls ripen twice yearly, some opening in June, others in 

 August ; this gave rise to the assumption that two gall-producing 

 generations occurred, the second of which was derived from eggs laid 

 by the winged forms of the first one. Further investigations have 

 shown that this is not a question of two generations, but of two 

 varieties ; an early one, C lapponicus var. pmecox, Choi., and a 

 late one C lapponicus var. tardus, Dreyfus. The var. praecox especially 

 resembles C. strobilobius, though radically differing in its life-cycle ; 

 (C208) o2 



