379 
1916-17.] The Family Chermesidae. 
C. A group in which migration is obligatory; two host plants are 
necessary, while the species are only slightly polyphagous. Here 
come a few Aphidinae, some Schizoneurinse and Pemphiginae. 
Here also come the Chermes species. 
Mordwilko’s theory is based on wide data, but it assumes that the same 
phenomena, within this diverse group (Aphids in its widest sense), arose in 
the same way. All the species of the Chermesidse, which possess a sexual 
generation, pass that generation on spruce. On the other hand, the 
parthenogenetic development has arisen on a number of other genera 
of conifers. In the author’s opinion the Blochmann theory explains this 
phenomenon in the more satisfactory way. 
In conclusion, I wish to express my indebtedness to Dr R. Stewart 
MacDougall for the help which he has given me in carrying out this 
research, and also to Professor I. Bay ley Balfour for facilities for obser- 
vation and experiment granted in the Royal Botanic Garden, Edinburgh. 
I am also indebted to the factors of the Right Hon. the Earl of Buchan 
for permission to carry out experiments at Drumshoreland, West Lothian. 
LITERATURE. 
(1) Blochmann, F., “Ueber die Geschlechtgeneration von Chermes abietis, L.,” 
Biol. Centralb., vii, pp. 417-420, 1887. 
(2) — “Ueber die regelmassigen Wanderungen der Blattlause speziell iiber den 
Generationscyklus von Chermes abietis , L.,” Biol. Centralb ., ix, pp. 271-284, 1889. 
(3) Borner, C., “ Systematik und Biologie der Chermiden,” TjOoI. Anz., xxxii, 
pp. 413-428, 1907. 
(4) “Eine monographische Studie iiber die Chermiden,” Arbeiien aus 
der Kais. Biol. Anstalt fur Land- und Forstwirtschaft , vi, 2, 320 pp., Berlin 
[P. Parey], 1908. 
(5) — “Ueber das System der Chermiden,” Zool. Anz., xxxiii, pp. 169— 
173, 1908. 
(6) “Ueber Chermesiden: ii, Experimenteller Rachweis der Enstehung 
diocischer aus mcinocischer Cellaren,” Zool. Anz., xxxiii, pp. 612-616, 1908. 
(7) “Ueber Chermesiden: iii, Zur Theorie der Biologie der Chermiden,” 
Zool. Anz., xxxiii, pp. 647-663, 1908. 
(8) “ Ueber Chermesiden : v, vi, vii, Cnaphalodes lapponicus , Choi.,” Zool. 
Anz., xxxiv, pp. 118-146, 1909. 
(9) “Zur Biologie und Systematik der Chermesiden,” Biol. Centralb., xxix, 
pp. 118-146, 1909. 
(10) Sorauer, P., Pjlanzen Krankheiten : III, Die tierischen Feinde, pp. 
654-683, Berlin [P. Parey]. 
