1 6 2 Sycamore gall. 



scutellum depressed, rugose in the centre, surrounded by 

 a well-marked smooth border. Abdomen shining, legs 

 yellow. Antennae with fourteen joints in the female, and 

 fifteen in the male. Colour similar in both sexes. 



In this generation the males and females are equal in 

 number, so that fecundation is secured before oviposition. 



I have not hitherto been successful in rearing this 

 generation ; the fecundated females descend the tree and 

 set about pricking not only the superficial roots but also 

 the base of the tree. I have no doubt that these galls 

 require two years for their development, in the same way as 

 Biorliiza aptera. 



As Pediaspis sorbi, Tischbein, and Bathyaspis aceris both 

 belong to the same generation-cycle, there is good reason 

 for abandoning Tischbein's name sorbi. There must have been 

 some confusion in the first discovery of this gall, for there is 

 no doubt that it is found only on the sycamore, and not on 

 the mountain ash as was then stated. 



A comparison of the two generations shows a sensible 

 divergence in size, in spite of natural characters otherwise 

 sufficiently similar. In the terebrae there is an essential 

 difference, rendered necessary by the nature of the work to 

 be done by each. The organization of the two generations 

 is also quite dissimilar ; the agamous lives three or four 

 weeks, while the sexual survives but a few days. 



Now if we unite the two generations in the same species, 

 as Dr. Mayr has just done, and with good reason, we ought 

 to remember that we are uniting two forms which are verj?^ 

 different. According to the ordinary tests of classification 

 we ought here to make of these two generations what 

 would be considered two ' good species.' And yet this 

 would be a wrong interpretation of facts which at present 

 we must be satisfied to observe. We are still in the stage 

 of observation ; and it must be left to some future generation 

 to undertake the explanation of the facts. 



SCHLESWIG, 



August I, 1 88 1. 



