No. 2.] THE DEVELOPMENT OF THE NEWT. 30 1 



Ruckert ('92) who finds a remarkable increase in bulk of the 

 chromosomes in the Selachian egg during the growth of the 

 (tgg, and an equally striking decrease premonitory of vesicular 

 dissolution. Ruckert considers this general atrophy of the 

 chromosomes as due to the withdrawal of the ovogrenetic or 

 "somatic" substance. The chromosomic material remaining 

 after the dissolution of the ovogenetic portion corresponds to 

 Weismann's Keimplasma. 



Ruckert draws an interesting comparison between the phe- 

 nomena observed by him in the Selachian Q^'g and the nuclear 

 phenomena discovered by Maupas and R. Hertwig in the 

 infusoria ('92, p. 134). In the behavior and functions of the 

 infusorian macronuclei and micronuclei he sees a close analogy 

 the phenomena displayed by the Selachian chromosomes. 



While admitting that such an interpretation may perhaps 

 hold for the Selachian egg I think that in the amphibian ovum 

 a somewhat different explanation must be sought after. The 

 chromosomes here undergo no extensive changes in bulk ; tJie 

 mtcleoli, however, do increase enormously in number and sice 

 during the anabolic period of maturation. I therefore believe 

 that in this case it is between the nucleoli and the macro- 

 nucleus of infusoria that a comparison, if such a comparison 

 have any value, can be most aptly drawn. 



It is now well established, thanks to the brilliant researches 

 of Maupas and Hertwig, that the infusorian micronucleus is 

 the bearer of the hereditary tendencies while the macronucleus 

 possesses a nutritive and regenerative significance. At the 

 time of the conjugation of ciliate infusoria the macronucleus 

 degenerates and totally disappears. The micronucleus takes 

 part in conjugation, and the daughter micronuclei give birth to 

 new macronuclei. 



A close parallel to this series of events is found in the 

 history of the amphibian nucleoli, (i) They arise if not from, 

 at least in intimate connection with the chromatin threads, the 

 presumable bearers of the germ plasm. (2) Their function 

 is almost certainly one of nutrition. (3) When the nucleoli 

 have ended their ovogenetic duties and the ovum is fully formed, 

 they degenerate and are dissipated throughout the vesicular 



