306 W. B. KIRKMAN AND H. S. BURR 



9. The second polar spindle is long and narrow. Its appear- 

 ance marks the end of maturation phenomena in the ovary, 

 and the termination of all development of the egg unless fertili- 

 zation occurs. 



10. In albino rats the chromatin of the first polar body is 

 scattered, that of the second polar body is massed. 



11. The very long middle piece of the sperm tail follows the 

 head into the cytoplasm of the egg. 



June 1913 



LITERATURE 



CoE, W. R. 1908 The maturation of the egg of the rat. Science, N. S., vol. 



27, no. 690. 

 Daniel, J. F. 1910 Observations on the period of gestation in white mice. 



Jour. Exper. Zool., vol. 9. 

 Donaldson, H. H. 1912 The history and zoological position of the Albino rat. 



Jour. Acad. Nat. Sci., Philadelphia, vol. 15, 2d series. 

 King, H. D. 1913 Some anomalies in the gestation of the albino rat (Mus 



norvegicus albinus). Biol. Bull., vol. 24. 

 Lantz, D. E. 1910 Natural history of the rat. Treas. Dept., Pub. Health and 



Marine Hosp. Service U. S., Washington. 

 Mark, E. L.,and Long, J. A. 1912 Studies on early stages of development in 



rats and mice. No. 3. Univ. California Pub. in Zool., vol.9, no. 3. 

 Miller, N. 1911 Reproduction in the brown rat (Mus norvegicus). Amer. 



Naturalist, vol. 45. 

 SoBOTTA, J. 1895 Die Befruchtung und Furchung des Eies der Maus. Arch. 



f. Mikr. Anat., Bd. 45. 

 SoBOTTA, J., u. BuRCKHARD, G. 1910 Reifuug und Befruchtung des Eies der 



weissen Ratte. Anat. Hefte, Bd. 42. 



PLATES 



Figures 1 to 4 and 7 to 18 were drawn with the camera lucida. All figures, 

 except 17 and 18 were drawn with Zeiss no. 4 oc. and xV oil immersion obj. giv- 

 ing a magnification of 1000 diameters. Figures 17 and 18 were drawn with a no. 

 6 oc. and tV oil imm. obj., giving a magnification of 1760 diameters. These 

 figures are reduced one-third, giving a magnification in the finished plate of 

 1174. All other figures are reproduced at the size drawn. 



PLATE 1 

 explanation of figures 



7 Shows an ovarian egg in the resting stage. The egg (Group II) has attained 

 approximately its greatest diameter. Nucleolus solid and deeply staining. Pro- 

 toplasmic bridges well marked. A follicle cell is shown dividing at^the left. 



8 An ovarian egg (Group III) at a slightly later stage showing the vacuoli- 

 zation of the nucleolus well started. 



