360 NATURAL SCIENCE. Nov., 



attained that stage of development at which it was clearly seen they 

 had arrived when the ovipositing must have actually taken place. 

 Here, then, was a case in which fact did not agree with theory ; our 

 business, therefore, was, by further observation and experiment, to 

 seek a solution of the difficulty. Accordingly, between the 16th of 

 July and the 13th of December, 1876, we made a daily examination 

 of buds from freshly-gathered twigs, by cutting these in section from 

 apex to base, so as to expose the interior of the bud. No trace of 

 eggs, however, appeared until the latter date, when the first group 

 was met with. Subsequently, they were found in increasing numbers 

 on each examination. In this way, between the dates referred to, I 

 myself bisected 4,100 of these buds, many of them being examined 

 under the microscope. Dr. Ransom, in like manner, opened 2,250, 

 together 6,350 in all. 



The sought-for result being thus arrived at, a new difficulty 

 presented itself. If the gall-producing cynips died, as it was found 

 to do early in July, how could it possibly lay its eggs in the December 

 following ? To this our own investigations gave no present answer ; 

 but a solution of the problem shortly came from Dr. Adler of 

 Schleswig, whose researches on the alternation of generations of Gall 

 Wasps (published in the ' ' Zeitschrift fur wissenschaftliche Zoologie " for 

 1880) established the fact that Tevas terminalis, in issuing from the gall, 

 proceeds not, as was supposed, to puncture the young buds of the 

 oak, but to make its way to the roots of the tree, and there to deposit 

 its eggs. In association with these a new and specific gall is formed, 

 from which, in due course, issues a swarm of females (and none but 

 females, for no male has ever yet been found) so unlike the parents 

 which produced them, as to have been classed by entomologists, not 

 simply as a different species, but as a distinct genus. These new 

 husbandless females are altogether destitute of wings, no nuptial 

 flight being called for, and have hence received the name of Biorhiza 

 apteva. 



Thus, between these two distinct and well-marked forms, we 

 have, as you will see, a conspicuous case of heterogenesis, or alter- 

 nation of generations — the bisexual giving rise to the agamic, the 

 agamic,- in its turn, to the bisexual. J 5 



Let us now follow one of these agamic females, and see the kind 

 of work she is called upon to do. Eating her way through the hard, 

 subterranean gall in which she has passed her successive metamor- 

 phoses, she struggles forward through the intervening ground, creeping 

 upwards to the now leafless branches of the oak. Here, by a dexte- 

 rous use of her terebra, preparatory to ovipositing, she makes a 

 transverse cut across the axis of a winter bud, above the circlet of 



15 In certain Lcpidoptcra (Psychida? and Tineidao) parthenogenesis appears to be a 

 normal process ; indeed, so far as known, the only process, for of some species the 

 males have never been found. (Herbert Spencer's " Biology," vol. i., p. 215.) This 

 agrees with C. kollavi and other of the " Cynipidae." 



