INBKEEDING, PARTHENOGENESIS, ASEXUAL REPRODUCTION 247 



tissue, while the other must penetrate deep down into the hard winter 

 bud, to be able to deposit its eggs in the proper place, and we there- 

 fore find that in the two kinds of female the ovipositor differs in 

 length, thickness, and general structure, and so also does the whole 

 complex apparatus by which the ovipositor is moved. But these 

 .differences are associated with the form of the abdomen, in which the 

 ovipositor lies, and with the strength and shape of the legs, which 

 must be shorter and stronger when the boring has to be performed 

 through a hard plant-tissue or to a considerable depth. We can 

 readily understand how numerous must be the secondary variations 

 which a transformation of 

 the ovipositor brings in its 

 train when we compare the 

 ovipositor apparatus in the 

 two generations of one of 

 these species (Fig. 126). 



Figure 126 shows the 

 ovipositor of another gall- 

 wasp, of which the winter 

 form, Nenroterus laeviuscu- 

 lus, also perforates the hard 

 winter buds of the oak, while 

 the summer form ,/Syx( th egadei ■ 

 albipes, lays its eggs in the 

 tender young leaves of the 

 same tree. The ovipositor of 

 the former is thin and long, 

 that of the latter short and 

 strong (Fig. 126, A and B), 

 and corresponding also to 

 the depth at which the egg 

 must be sunk, or, so to speak, 



sown in the tissue of the plant, the egg of the summer generation 

 differs from that of the winter generation by having a much 

 shorter stalk (Fig. 126, ei). These little wasps thus afford a beautiful 

 example of the way in which even marked changes in the condi- 

 tions of life of a generation may be associated with transformations 

 in bodily structure, and we understand how it was possible that 

 by means of processes of selection the generations which alternate 

 periodically in the year should come to diverge very considerably 

 in structure. The example may also serve to illustrate how diverse 

 are the harmonious co-adaptations which such transformations require. 



B 



Fig. 126. Ovipositor and ovum of the two 

 generations of the same species of Gall-wasp. 



A, those of the winter form, Neuroterus heviusculus. 



B, those of the summer- form, tSpathegaster albipes. 

 st, ovipositor, ei, ovum. Similarly magnified. 

 After Adler. 



