The Scottish Naturalist, 153 



Aulax, the first eight being exclusively confined to the oak, 

 and the last three to other plants. He furthermore pointed 

 out that among certain genera there were absolutely no males, 

 while with others the two sexes were in nearly equal propor- 

 tions ; Cynips, (or Cynips, Dryophanta, and Aphilothrix, as now 

 restricted by Foerster) Synophrus, Biorhiza, Neuroterus (except 

 some parasitic species of doubtful generic location) being in the 

 former predicament. 



To a very great degree the evidence proving the unisexual 

 condition of these insects is to a more or less extent of a nega- 

 tive nature, and consists mainly in many thousands of them 

 having been reared from their respective galls, by competent 

 naturalists all over Europe, without a single male having been 

 discovered. But the evidence is not entirely of this negative 

 character. Mr. F. Smith took some galls of Cynips Kollari 

 to a locality where they were previously unknown, and that 

 species was soon located there. I have repeated myself this 

 experiment with single galls of Kollari, and also with 

 Aphilothrix radicis, with entire success. So that, granting that 

 no dimorphism occurs, we are quite justified in concluding that 

 no males exist, or if they do they must appear at long intervals 

 and in very limited numbers. 



It is to be noted also that the bisexual species are as a whole 

 vernal, the galls appearing with the young leaves and flowers, 

 and the insects pass with great rapidity through their transfor- 

 mations, some of them reaching the perfect state in 3 weeks 

 after the appearance of the galls. The agamic species again 

 are mostly autumnal, and their galls are much harder, larger, 

 and of a more complicated structure than the others. 



Briefly stated. Dr. Adler's hypothesis is that the bisexual spring- 

 forms oviposit on their exclusion in early summer, and give origin 

 in the autumn, not to galls and insects like themselves, but to 

 totally different galls, which yield agamic forms very dissimilar to 

 the spring ones, and these autumnal insects hibernate, and lay 

 their eggs in early spring, which in due time yield the bisexual 

 flies. Thus, he states that Spaihogaster baccarum, the maker of 

 the common " Currant galls," oviposits in the young leaves, pro- 

 ducing the well known " spangle galls " of Neuroterus lenti- 

 adaris, which in the spring lays its eggs in the buds, giving 

 issue to the "Currant galls." In the same way Alder connects 

 Neuroterus fumipennis with Spaihogaster albipes 

 „ 7iu7?iis7?iatis „ ,, vesicat?ix 



