2 74 Experimental Zoology 



begins to develop, in the middle of which sits the stem-mother. 

 She soon begins to give birth, parthenogenetically, to offspring 

 v^hich also remain in the gall, and in some cases hundreds of 

 individuals almost filHng 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 preexisting 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 



Abler, 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. 

 Bedlard, a. de. Influence de la lumiere 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. 

 Billon, M. M. F., et Stassand, F. Action de quelques composes phos- 



phores sur la nutrition. Comp. Rend, de la Soc. Biol. LV. 1903. 

 Blanc, L. Note sur les effets teratogeniques de la lumiere blanche sur 



I'oeuf de poule. Compt. Rendus de Biol. Paris, XLIV. 1892. 

 BosCHER. Die Beziehung der Wachthumsgeschwindigkeit des Saug- 



lings zur Zusammensetzung der Milch bei verscheidenen Saugethie- 



ren. Zeitschr. f. physiol. Chemie, XXIV. 



