Katharine Foot and E. C. Strobell 215 



Plate IV, 86 to 89, Plate V, we find the chromosomes in a tangled condi- 

 tion, and we are iniable to identify- in such confused masses of chromo- 

 somes the rings or other forms of an earlier stage (Photos. 51 and 52, 

 Plate III). Presumably the small ring of Photo. 52 answers to the small 

 four part chromosome of Photo. 72, Plate IV, and perhaps to the small 

 chromosome of Photos. 33, Plate II, 91, Plate V, and 99, Plate VI, but 

 our sections give no proof of this, chromosomes being so rarely isolated 

 in fixed material that no trustworthy comparison of progressive stages 

 can be made. 



In dried germinal vesicles, however, the chromosomes of each stage 

 are clearly isolated and can be readily compared and a few of the chromo- 

 somes of the first maturation spindle can be identified in the prophases, 

 though their individual differences are not sufficiently marked to make 

 such identification conclusive. 



In the majority of cases the photographs of sections show that the 

 chromatic filaments are partly formed, more or less at the expense of the 

 reticnlum in which they are iml^edded (Photos. 22 to 25, Plate II, 46 to 

 49 and 59 to 62, Plate III). We are convinced that this is not com- 

 parable to the living condition; but due to fixation, for its degree varies 

 with different fixatives. Eggs fixed in chromo-acetic show the extent 

 to which this process can be carried, the achromatic substance " and 

 chromatin being coagulated into thick, loose coils that are so dense they 

 hold the stains with as much tenacity as the chromosomes (see Photo. 

 34, Plate II). This photograph also shows the nuclear membrane dis- 

 torted and torn, whereas the membrane of the germinal vesicles of eggs 

 killed in platino-osmic remains unbroken and in perfect contact with the 

 nucleoplasm as well as the cytoplasm. Compare for example. Photo. 34, 

 Plate II, with Photos, 68 and 69, Plate IV, the latter egg showing the 

 smooth contour of the memljrane typical of a living egg, and this is also 

 shown in germinal vesicles dried on the slide. 



All the sections of germinal vesicles are photographed at the same 

 magnification (1000) and a comparison of any of them with Photo. 34, 

 Plate II, demonstrates the swelling of the germinal vesicles in the 

 chromo-acetic preparation. Watching the effect of chromo-acetic on the 

 living egg under the microscope shows that this fixative first swells the 

 ^gg before the usual shrinkage of dehydration commences — the final 

 shrinkage being less than that of many other fixatives. The actual size 



^= "We use the expression achromatic substance because it is so well estab- 

 lished as a definite part of the nucleoplasm as distinct from chromatin. It 

 is often, however, a misnomer, for in some cases it stains intensely (Photos. 

 27 and 28, etc.). 



