No. 2.] THE EGG OF BUFO LENTIGINOSUS. 32 1 



the nucleoplasm breaks up into granules and stains like them, 

 thus making it impossible to follow their further history. 

 Only a much more extended study of the nucleoli in the ^^g 

 of Bufo can determine which of the various explanations that 

 have been advanced to account for the presence of these bodies 

 is substantiated by facts. 



7. CJiromatin Red?iction. 



Several prominent investigators have recently emphasized 

 the fact that the question of reduction involves more than a 

 separation of the chromosomes during the two polar divisions, 

 and they have asserted that the key to the solution of the prob- 

 lem is to be sought in the origin of the so-called tetrad groups. 



In the egg of Bufo the question is a most perplexing one, 

 owing to the peculiar changes occurring during the formation of 

 the first polar spindle. As the substance which forms the irreg- 

 ular masses near the first polar spindle is undoubtedly chromatin, 

 fully one-half of the cJiromatin substance of the germinal vesicle 

 does not go into the chromosomes of the first polar spindle. On 

 Hertwig's ('90) assumption that reduction is " eine Einrichtung 

 um zu verhindern dass durch die Befruchtung eine Summirung 

 der Kernmasse und der chromatischen Elemente herbeigefuhrt 

 werde," it is not conceivable why the mechanism of karyoki- 

 nesis should be called upon to lessen again the amount of chro- 

 matin. If we disregard these masses and consider only the 

 chromatin material which forms the twelve chromatin rings of 

 the first polar spindle, then the problem is somewhat simplified. 

 Judging from the results which have been obtained by a study 

 of other eggs, it seems highly probable that the paired arrange- 

 ment of the chromosomes in the early maturation stages of the 

 toad's egg is brought about by a longitudinal division of chro- 

 matin threads existing in the germinal vesicle from the time of 

 the formation of the oocyte. Riickert ('92), who has met with 

 the same paired arrangement of chromosomes in the ovarian egg 

 of the selachian,'states that " Die Verdoppelung geschieht beim 

 Uebergang des Ureies zur Eimutterzelle und zwar, wie sich 

 mit Wahrscheinlichkeit darthun lasst, durch eine eigentumliche 



