220 ENTOMOLOGICAL NEWS. [September, 



DEPARTMENT OF EGONOMIG ENTOMOLOGY. 



Edited by Prof. JOHN B. SMITH, Sc. D., New Brunswick, N. J. 



Alternating Generations. A Biological Study of Oak Galls and Gall Flies. 



By Hermann Adler, M.D., Schleswig. Translated and edited by Chas. 

 R. Straton, F. R. C. S., F. E. S., Oxford, at the Clarendon Press. New 

 York, Macmillan & Co., pp. xi, et 198, 3 pi., col. 



Under the above title we have an extremely interesting and valuable 

 work, to which both author and translator have contributed a series of 

 careful observations that much enlarges our knowledge of the subject 

 under consideration. 



The subject of parthenogenesis among insects is a most attractive one, 

 and offers great fields for original work; none of them wider than among 

 the Cynipidae, where it appears in a variety of forms, alternating with 

 normal sexual reproduction in many instances; but frequently established 

 as a constant feature in the life cycle of the species. In a rather lengthy 

 introduction the translator discusses the general subject and sketches 

 historically the investigations made, the conclusions reached, and the 

 theories upon which the phenomena have been explained. He describes 

 the formation of the reproductive cells in both sexes, the modifications 

 that they undergo, and cites cases of spermatogenesis to prove that po- 

 tentially the male cells may be reproductive, while the possibility of con- 

 tinued agamic reproduction is theoretically demonstrated. 



The author first cites the observations therefore made on the alternation 

 of generations among oak gall-flies, explains the methods by which his 

 own observations were made, and then gives in detail the records of a 

 long series of experimental breedings, proving conclusively that the spe- 

 cies of certain genera are merely agamous forms of those of other genera, 

 and, finally, that in certain other forms males never appear, the agamous 

 females ovipositing freely and the eggs proving fertile in all cases. An 

 interesting chapter is devoted to the formation of the galls, proving that 

 the adult does nothing to influence it. " Hitherto it has constantly been 

 stated that the prick of the gall-fly and the simultaneous introduction of 

 a glandular secretion excited a specific cell growth which led to the for- 

 mation of the gall. This, I hold, only begins when the larva emerges from 

 the egg." " The moment the larva has broken through the egg covering, 

 and has for the first time wounded the surrounding cells with its delicate 

 mandibles, a rapid cell-growth begins." Observations made substantiate 

 this conclusion; but it is limited in its application to Cynipid oak-galls 

 because numerous exceptions exist in other groups. A detailed descrip- 

 tion of the ovipositor is given, the method of its use is observed and the 

 function of the peculiar egg stalk in this family is made clear. 



Finally, a chapter is devoted to an explanation of the reasons for this 

 alternation of generations and how it was originated ; the conclusion 



