No. 2.] THE DEVELOPMENT OF THE NEWT. 303 



remember the sharp differences in chemical reaction dependent 

 on apparently slight differences in chemical constitution. 



(3) There is much greater unanimity of opinion concerning 

 the fate of the nucleoli of the egg-cell than concerning either 

 their origin or significance. The nucleoli always degenerate 

 and disappear before the process of fertilization. 



Thus in origin, function, and fate many of the bodies called 

 nucleoli constantly suggest community of relationship with the 

 infusorian macronucleus. We are, however, hardly at present 

 in a position to know whether this resemblance is superficial or 

 fundamental. 



The interesting case brought forward by Riickert, and al- 

 ready touched upon, may be considered as consonant with the 

 analogy just drawn. It may be supposed that the fluctuations 

 in the bulk of the Selachian chromosomes are due to a certain 

 proportion of ovogenetic (nucleolar .'') substance remaining at- 

 tached to the chromosomes and never becoming separated as 

 true nucleoli. This modification of his view allows it to be 

 brought into harmony with other ovogenetic observations. It 

 is worthy of notice that Riickert observes and remarks upon 

 the close parallelism of development between Selachian nucleoli 

 and chromosomes. 



TJie atrophy of tJic germinal vesicle and the formation of the 

 polar bodies. — The principal changes that take place in the 

 germinal vesicle before the ^^^ leaves the ovary have been 

 already described. The germinal vesicle in Fig. i 5 has nearly 

 reached the limit of the changes which it undergoes while the 

 Q%g is still in the ovary. The oldest nuclear appearance that 

 I have found in an ovarian o^g'g very closely resembles that 

 shown in Fig. 15, except that the chromosomes are slightly 

 stouter and more distinct, and are massed together in the 

 center, while at the same time the borders of the vesicle show 

 an incipient invasion of yolk spheres. Between such an ap- 

 pearance and the well-defined maturation spindle, shown in 

 Figs. 18 and 21, I have found no intermediate stages, although 

 I have made careful serial sections through a number of eggs 

 showing a light spot externally and apparently just ready to 

 break loose from the ovary. The transition is evidently an 



