Hubbard] *^ [Dec. 15, 



the nucleus, and during the remainder of the egg's immaturity gradually 

 moves away from tlie nucleus. From this fact and its early relation to the 

 nucleus it seems evident that it must have originated from the nucleus. Bat 

 there is another more potent proof that this is its origin. The largest eggs 

 in the young fishes 17 mm., 89 mm., 35 mm. and 40 mm. in length mea- 

 sured as follows : 



Diameter of egg 35 //. Diameter of nucleus 20 /u. 



" 30//. " " 171//. 



" 25//. " " 15 /i. 



In other vFords, the diameter of the nucleus is more than half the diameter 

 of the egg. It will be remembered that none of these eggs contained a 

 yolk nucleus. The smallest eggs in the adult fish containing a yolk nu- 

 cleus measured as follovps : 



Diameter of egg 20 //. Diameter of nucleus 10 //. 



25/1. " " 12^//. 



30 /A " " 15//. 



That is, the nucleus has now been reduced to a diameter equal to one- 

 half that of the egg. If this body originates from the nucleus as an ex- 

 trusion of a part of its substance we should expect the nucleus to be rela- 

 tively larger to the size of the egg before it appears than after its appear- 

 ance. This is exactly the case in these eggs (compare nucleus in Fig. 

 la and Fig. 3). It will be seen from the two sets of measurements given 

 above that in the eggs in which this body is not visible the diameter of 

 the nucleus is always more than AaZ/that of the egg, while in the eggs in 

 which it is visible the diameter hjust half that of the egg. This relation 

 is true in all the measurements I made. 



Take an egg with a diameter of 25 /< as a typical size of the smallest 

 eggs in the adult fish and the largest in the small fish. To simplify opera- 

 tions I have taken the number of divisions of the mikrometer instead of 

 the absolute measurement of the egg. Then the sizes of the eggs are ex- 

 pressed as follows : 



Diam. of egg in adult fish («) 5. Diam. of nucleus 2^. 



" " small " ....(o)5. " " 3. 



The dark body (e) in the protoplasm of the egg being an oblate spheroid 

 measures 2 in conjugate axis and 2.375 in tranverse axis. 



Now the solid contents of the nucleus in o ought to equal the solid con- 

 tents of the nucleus s, plus the solid contents of the dark body e, or o = 

 s -\- e. 



Formula for contents of a sphere is V = i ;r D\ 



" " " " oblate spheroid \s \/ = ^ - a'^ b. 



V = volume. 



D = diameter. 



a = semi-transverse axis. s 



b = semi-conjugate axis. 



