586 



HEMIPTERA-HOMOPTERA 



CHAP. 



known as parallel series. This has been recently investigated in 

 the genus Chermes by Blochmann, Dreyfus, and Cholodkovsky. 

 This latter savant informs us l that a wingless parthenogenetic 

 female of Chermes hibernates on a fir-tree Picea excel sa and 

 in the spring lays numerous eggs ; these hatch, and by the effects 

 of suction of the Chermes on the young shoots, galls are formed 



(Fig. 286), in which the Insects are 

 found in large numbers ; when they 

 have grown the galls open, and allow- 

 ing the Insects to escape these moult 

 and become winged females. They 

 now take on different habits ; some of 

 them remain on the Picea, lay their 

 eggs thereon, and out of these there 

 are produced young that grow into 

 hibernating females, which next spring 

 produce galls as their grandmothers 

 did ; but another portion migrates to 

 the Larch (Larix) ; here eggs are laid, 

 from which proceed wingless partheno- 

 genetic females, that hibernate on their 

 new or secondary plant, and in the 

 following spring lay their eggs and 



FIG. 285. Chermes alnetis; hilier- ' J 



nating female or "winter- give rise to a dimorphic generation, 

 mother." Europe Much mag- t f th becoming nymphs and 



nifaed. (After Cholodkovsky. ) , . . 



going on to the winged condition, 



while the other part remain wingless and lay eggs, that give rise 

 to yet another wingless generation ; in fact, a second pair of parallel 

 series is formed on the new plant, of which one is wingless, and 

 exclusively parthenogenetic, and continues to live in this fashion 

 for an indefinite period on the secondary plant, while the other 

 part becomes winged ; these latter are called sexuparous, and go 

 back to the Picea, and there lay eggs, that give rise to the 

 sexual forms. If we would summarise these facts with a view 

 to remembering them, we may say that a migration of a part of 

 a generation from the Picea was made with a view of producing 

 a sexual generation, but that only a portion of the migrants suc- 

 ceeded in effecting the object of the migration, and this only in 

 their third generation. Thus portions remained on the Picea, 



1 LLorae Soc, e.nt. Ross. xxiv. 1890. p. 386. 



