Kathariue Foot and E. C. Strobell 213 



chromosomes are formed, e. g., Photos. 121 to 124, Plate VIII, but 

 Photos. 116 to 118, Plates VII and VIII demonstrate that the disap- 

 pearance of the principal nucleolus may be retarded until after the com- 

 plete formation of the chromosomes. Such cases demonstrate that the 

 chromosomes in Allolohophora are not formed at the expense of the 

 nucleolus. Korschelt, '95, has reached a like conclusion for the Annelid 

 Opliryotroclia and in its morpholog}^ the large nucleolus of Opliryo- 

 iroclia is strikingly like the large nucleolus of Allolohophora (compare 

 Korschelt's figures of the germinal vesicle 72, 74, 75 and 79 with our 

 Photos. 29, Plate 11, 49, 58, Plate III). On this point observations on 

 a number of Annelids are in accord (compare Myzostoma, Wheeler's 

 Figs. 3 and 4, '97, TJialasscma, Griffin's Figs. 3, 6 and 8, '99). In 

 Batracliians, Lubosh, '02, has supported his criticism of the nucleolar 

 origin of the chromosomes by a reproduction of many interesting photo- 

 graphs of the nucleoli in Triton eggs. A few of them resemble those 

 of Allolohophora, cf. his Photo. 8 with our Photos. 5, 14a, and 75, Plate 

 IV, also his Photos. 5 and 18 with our 20, Plate I, 54 and 55, Plate III. 



Chromatix. a Comparative Study of Sections and of Entire 

 Germinal A'esicles dried on the. Slide. 



The photographs of the germinal vesicles of Plates I to IV show the 

 average results obtained by sectioning these eggs after killing them in the 

 ^ ariety of fixatives given on jj. 200. 



The photographs of Plates VII, VIII and IX show the average results 

 obtained by drying individual germinal vesicles on the slide, according 

 to the method described on p. 200. A comparison of these two sets of 

 photographs demonstrates the advantage of the latter method, the former 

 proving inadequate almost to the point of being misleading, and it is 

 here evident that we have not yet found a fixative for this egg that shows 

 the development of the chromosomes as clearly as they are demonstrated 

 in dried preparations. 



In sections, the chromatin of the most mature eggs of the ovary and of 

 the youngest eggs of the receptacula ovorum, is at about the same 

 stage of development, the relatively achromatic reticulum of the germinal 

 vesicle showing only indefinite chromatic aggregations wliich appear 

 to be the first steps towards forming the filaments out of which the 

 eleven bivalent chromosomes are finally formed. The first indications 

 of chromatic filaments are shown in Photos. 1 to 9, and 31, Plate II, and 

 60. Plate III. 



In dried germinal vesicles an early stage of the aggregation of chro- 



