210 First IMaturation Spindle of Allolobophora Foetida 



We hesitate to interpret the accessory chromosome of some authors 

 as the equivalent of the accessory nucleolus, but it is a suggestive fact 

 that many investigators have interpreted this structure as a nucleolus 

 and there is a significant disagreement as to whether it divides in the 

 first or second spindles, or in fact whether it divides at all. Our inter- 

 pretation that the accessory nucleolus of Allolobophora is the true 

 nucleolus of the oocyte second order supports Wilson's, '96, surmise that 

 the accessory nucleoli of egg cells "perhaps correspond to the true 

 nucleoli of tissue cells'' (p. 93), though he bases this conclusion on his 

 interpretation that the principal nucleolus does not correspond to the 

 " true nucleoli of tissue cells." " He mentions two kinds of nucleoli 

 in Qgg cells, the "principal nucleolus," or net knot, and the "accessory 

 nucleoli," which are of the second (smaller) type, and although they do 

 not agree in their affinity for stains with the accessory nucleoli of 

 Allolohophora (which at this stage stain with greater intensity than the 

 principal nucleolus and retain the color with more tenacity even than 

 the chromosomes), they do agree in other more essential points, i. e., in 

 their relation to the single large nucleolus as to size, number, advent 

 and persistence. In a later edition of " The Cell " ('00) , Wilson's conclu- 

 sions are greatly modified and he states that the principal and accessory 

 nucleoli " differ widely in staining reactions, but it does not 3^et clearly 

 appear whether they definitely correspond to the plasmosomes and karyo- 

 somes of tissue cells." He further says that the principal nucleolus 

 " cannot be directly compared to the net knots or karyoso\nes of tissue 

 cells," leaving the implication that they resemble the true nucleoli 

 (plasmosomes) of tissue cells, although he adds that in color reaction the 

 accessory nucleoli are comparable to these, pp. 127 and 128. 



In Cliaiopterus, Mead, '98, figures a ring-shaped nucleolus (Fig. 6) 

 closely resembling those of Allolohophora, and although he says nothing 

 of accessory nucleoli he has demonstrated in several of his figures two or 

 three nucleoli which appear to answer to the accessory nucleoli of Allolo- 

 hophora. He says the nucleolus " breaks up into a number of pieces 

 which remain for a time in the vicinity of the spindle, but gradually 

 degenerate and disappear," p. 196. In Allolohophora it is the acces- 

 sory nucleoli which often persist until after the first maturation spindle 

 is formed, the principal nucleolus disappearing at an earlier period. 



10 << Prom its staining-reaction this type of nucleolus appears to correspond, 

 in a chemical sense, not with the ' true nucleoli ' of tissue cells, but with 

 the net knots or karyosomes, such as the nucleoli of nerve cells and of many 

 gland cells and epithelial cells," p. 92. 



