116 The (rails of Kssex ; a Contribution to a 



support of the metagenesis theory mentioned by Dr. Rein- 

 hard ^^ as more probable than the dimorphic hypothesis which 

 had previously been foreshadowed by Osten-Sacken^^ and in 

 Walsh's papers in the ' Proceedings ' of the Entomological 

 Society of Philadelphia. '^^ Bassett writes that " from all the 

 above facts I infer that all our species that are found only in 

 the female sex are represented in another generation by both 

 sexes, and that the two broods are, owing to seasonal diffe- 

 rences, produced from galls that are entirely distinct from 

 each other." This hypothesis has now been proved to be the 

 true gall-fly history, and in the Cynipidae we have very dis- 

 tinct exponents of the metagenesis theory or so-called " alter- 

 nation of generations," which we know is so generally the 

 case with the Scolecida and Hydrozoa.^*^ Dr. H. Adler first 

 actually proved the fact with Neuroterus le7iticularis smd Spathe- 

 gaster haccarum,^^ and this important discovery has been 

 followed up with other researches made with various gall- 

 flies on numerous small oak-trees planted in pots ; the theory 

 has thus been established in 19 — really 38 — distinct species. 

 This has revolutionised the whole history of the Cynipidae. 

 Dr. Adler' s remarkable memoir ,^^ detailing his observations 

 and with notes on the structure of both the galls and gall- 

 s' " Die Hypothesen liber die Fortpflanzungsweise der eingeschlechtigen 

 Gallwespen." ' Berliner Entomologische Zeitschrift.' Vol. ix. (1865). 



35 "Ueber die Gallen und andere durch Insecten hervorgebrachte Pflan- 

 zen-deformationen in Nord- America." By Baron Osten-Sacken. ' Stettiner 

 Entomologische Zeitung,' vol. xxii., pp. 405 — 423 (Oct. — Dec, 1861). 



86 Vol. i., pp. 47—72 (Oct., 1861) ; pp. 241—259 (Sept., 1862). Vol. ii., 

 pp. 33—49 (April, 1863) ; pp. 443—500 (March, 1864). Vol. iv., pp. 

 331—380 (May, 1865). 



87 [The words " cyclical propagation," introduced into England by Mr. 

 Meldola in his Annual Address to the Essex Field Club (Jan. 12th, 1882), 

 to denote the idea hitherto known by the awkward phrase " alternation of 

 generations," are so much more convenient, and so neatly express the 

 true nature of the phenomena, that they should be adopted in future by 

 all biologists. — Ed.] 



as ' Deutsche Entomologische Zeitschrift' xxi. 209—248 (1877). 



'3 "Uberden Generationswechsel der Eichen-Gallwespen." ' Zeitschrift 

 fiir wissenschaftliche Zoologie,' vol, xxxv,, pp. 151 — 246 ; pi. x., xi., xii. 

 (1880). 



