lv CONTENTS 
Ivan E. Wauuin. On the nature of mitochondria. III. The demonstration of mito- 
chondria by bacteriological methods. IV. A comparative study of the morphogenesis 
of root-nodule bacteria and chloroplasts. Two plates (nine figures)............... 451 
A. W. Bretuamy. Differential susceptibility as a basis for modification and control of 
development in the frog. II. Types of modification seen in later developmental 
stager. ‘sS¢eventy steures Kat eae as eis he ae a eaiGr.\feialtns.' Jo eae 473 
A. L. Sauazar. Sur une forme particuliére d’atrésie des follicules de deGraaf (lapine), 
révélée par la méthode tannoferrique. Cinq figures................ ee eee e ee eee eens 503 
