350 DEVELOPMENT OF ELASMOBRANCH FISHES. 



The normal full-sized ova exhibit the following structure. 

 They consist of a mass of somewhat granular protoplasm of 

 irregular, but more or less rounded, form. Their size varies 

 from 'Oi6 '036 Mm. In their interior a nucleus is present, 

 which varies from x>i2 '016 Mm., but its size as a rule bears no 

 relation to the size of the containing cell. 



This is illustrated by the subjoined list of measurements. 



Size of Primitive ova in Size of nucleus of Primitive 



degrees of micrometer scale ova in degrees of micrometer 



with F. ocul i. scale with F. ocul i. 



10 8 



13 8 



13 



H 7 



IS 7 



13 7\ 



ii 8 



16 5i 



12 7 



10 7 



15 6 



13 6 



12 7 



The numbers given refer to degrees on my micrometer scale. 



Since it is the ratio alone which it is necessary to call attention 

 to, the numbers are not reduced to decimals of a millimeter. 

 Each degree of my scale is equal, however, with the object glass 

 employed, to '002 Mm. 



This series brings out the result I have just mentioned with 

 great clearness. 



In one case we find a cell has three times the diameter of 

 the nucleus 16 : 5^ ; in another case 10 : 8, the nucleus has 

 only a slightly smaller diameter than the cell. The irration- 

 ality of the ratio is fairly shewn in some of my figures, though 

 none of the largest cells with very small nuclei have been 

 represented. 



The nuclei are granular, and stain fairly well with haema- 

 toxylin. They usually contain a single deeply stained nucleolus, 

 but in many cases, especially where large (and this independently 



