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



polar body is, in all probability, always larger than the second, 

 though disintegration may set in immediately upon its formation. 

 The second polar spindle as seen in the ovary is much longer 

 and narrower than the first, but resembles the first polar spindle 

 in having open ends and no centrioles. The chromosomes in 

 the second polar spindle are almost always spherical. 



TUBE EGGS 



The living unsegmented egg of the albino rat measures about 

 0.079 mm. in diameter (the exact size varies a few thousandths 

 of a millimeter in different specimens), and is surrounded by a 

 zona of transparent jelly about 0.022 mm. in thickness. The 

 two unsegmented rat eggs that were obtained sufficiently free 

 from follicle cells to be available for detailed study, both pos- 

 sessed two polar bodies, measuring in one specimen 0.019 and 

 0.0132 mm. in diameter respectively, and in the other specimen 

 0.008 and 0.0065 mm. These eggs while translucent were filled 

 with highly refracting globules scattered through the protoplasm. 

 In one egg there was a clear area near the center, where we 

 thought we could distinguish the two pronuclei lying side by 

 side. 



The rare occurrence of the first polar body associated with 

 the egg in the tube is to be attributed to its rapid disintegration, 

 which, as already stated, begins almost as soon as it is formed, 

 and may lead to its complete disappearance before ovulation 

 occurs. A stained and sectioned tube egg, accompanied by the 

 first polar body, is shown in figure 12. This polar body is very 

 small, contains only a little stainable chromatin scattered through 

 it, and its protoplasm is much denser than that of the egg. 



Until after fertilization, and if this fails to take place until it 

 degenerates, the chromatin of the second -polar spindle remains 

 in a clearly defined equatorial plate, but in the egg in the Fallo- 

 pian tubes, this spindle always appears much longer and thinner 

 than in the ovarian eggs. 



The rat spermatozoon has an exceedingly long tail (fig. 16 a), 

 and like that of the mouse carries more or less of its tail with it 



