136 David Day Whitiiey 



Lyon, E. P. '06 — Some Results of Centrifugalizing the Eggs of Arbacia. Amer. 



Journ. Physiol, xv. 

 Morgan, T. H. '06 — The Influence of a Strong Centrifugal Force on the Frog's 



Egg. Arch. f. Entw. Mech., xxii. 

 '07 — The Effect of Centrifuging the Eggs of the Mollusc, Cumingia. 



Science, n. s., vol. xxvii, no. 680, pp. 66-67. 

 Morgan and Lyon '07 — The Relation of the Substances of the Egg, separated 



by a Strong Centrifugal Force, to the Location of the Embryo. 



Arch. f. Entw.-Mech., xxiv. 

 Wetzel, G. '04 — Centrifugalversuch an unbefruchteten Eiern von Rana fusca. 



Archiv. f. mikr. Anat., Ixiii. 



DESCRIPTION OF PLATE 



Fig. I Section of a centrifuged egg, showing the three zones and the germinal vesicle located near 

 the boundary of the pink and the clear zones. Gilson mercuro-nitric fixing fluid and Heidenhain's iron 

 haematoxylin stain. 



Fig. 2 Section of a centrifuged egg showing the three zones and the maturation spindle in the 

 clear zones. Yolk granules are lodged against the achromatic figure. Bouin's fixing fluid andHeiden- 

 hain's iron haematoxylin stain. 



Figs. 3 to 6 Free hand semi-diagramrnatic drawings of living eggs in the first cleavage stage which 

 were centrifuged when in the oviducts of the females. The fine stippling shows the position of the 

 pink zone, the coarser stippling shows the position of the gray zone, and the clear space indicates the 

 clear zone. 



Fig. 3 Experiment XXXI — The pink zone included in the small cell and the gray and clear zones 

 are in the larger cell. 



Fig. 4 Experiment XXXVII — About one-half of the pink zone and a portion of the clear zone 

 included in the small cell and the other part of the pink zone, all the gray zone, and a part of the clear 

 zone are included in the larger cell. 



Fig. 5 Experiment XXXII — Portions of each of the three zones in each of the two cells. 



Fig. 6 Experiment L — About two-thirds of the gray zone included in the small cell while the 

 other third of the gray zone together with all of the pink zone and nearly all of the clear zone are included 

 in the larger cell. 



