274 Experimental Zoology 
begins to develop, in the middle of which sits the stem-mother. 
She soon begins to give birth, parthenogenetically, to offspring 
which also remain in the gall, and in some cases hundreds of 
individuals almost filling the interior are produced in one or 
more generations. These also suck the juices of the plant by 
thrusting their proboscides into the inner walls of the gall. 
The gall may continue to grow during the whole summer, but 
generally its full size is soon attained. The winged insects 
emerge from a preéxisting opening in the gall, or in some cases 
the gall bursts when the inmates are mature. The phylloxerans 
produce galls on the leaves of hickories and other trees, and 
on the roots of the grape vine. Large bottle-shaped galls are 
produced by aphides on the elm; the coxcomb galls of the elm 
also owe their origin to them. The cause of the development of 
the galls in these cases is entirely unknown. Possibly the 
stem-mother and her offspring that suck the juices of the plant 
by thrusting their beaks into the inner walls of the gall may 
secrete some fluid that acts on the tissues of the plant. 
LITERATURE, CHAPTER XVI 
ADLER, H. Ueber den Generationswechsel der Eichengallen. Zeitschr. 
f. wissen. Zoologie, XXXV. 1881. (Translated by C. R. Stratton. 
Clarendon Press, Oxford, 1894.) 
BarFurTH, D. Versuche ueber die Verwandlung der Froschlarven. 
Archiv. f. mikr. Anat. XXIX. 1887. 
Bepiarp, A. DE. Influence de la lumiére sur les animaux. Compt. 
Rendus, XLVI. 1858. 
BEYERINCK, M. W. Beobachtungen ueber die ersten Entwickelungsphasen 
einiger Cynipidengallen. Verhandl. d. k. Akad. d. Wetenschappen 
Amersterdam, XXII. 1883. 
Die Galle von Cecidomya an Poa nemoralis. Botan. Zeit. XLIII. 
1885. 
Ueber das Cecidium von Nematus Cupreae auf Salix amygdalina. 
Botan. Zeit. XLVI. 1888. 
Bitton, M. M. F., et Stassanp, F. Action de quelques composés phos- 
phores sur la nutrition. Comp. Rend. de la Soc. Biol. LV. 1903. 
Branc, L. Note sur les effets teratogéniques de la lumiére blanche sur 
l’ceuf de poule. Compt. Rendus de Biol. Paris, XLIV. 1892. 
Boscuer. Die Beziehung der Wachthumsgeschwindigkeit des Siug- 
lings zur Zusammensetzung der Milch bei verscheidenen Saugethie- 
ren. Zeitschr. f. physiol. Chemie, XXIV. 
