142 BULLETIN OF THE 



IV. Degenerative Changes. 



Plate II. Figs. 14, 24-36 . Plate III. Figs. 28, 34. 



The striking difference in the appearance of cells and nuclei, and 

 the different manner of division of the nuclei, exhibited by serosae of 

 different ages, have frequently been referred to. Sucli changes, in 

 part at least, I believe to be due to degeneration of the membranes, 

 which, with the exception of the ovarian capsule, are temporary struc- 

 tures, soon to be cast off by the embryo. Hence it is not surprising to 

 find them undergoing degeneration in toto. The degenerative changes 

 are about equally well marked in all three membranes ; but on account 

 of the great size of cells and nuclei, the changes are most conspicuous in 

 the serosa. If tlie membrane comes from a young embryo, the walls 

 of the cells ax'e unstainable, and therefore often difficult to make out. 

 The nuclei have a vesicular appearance, with smooth, rounded contour, 

 abundant karyoplasm, and scanty chromatic substance. For this reason 

 the nuclei seldom stand out clearly from the cytoplasm in a stained 

 preparation, often being no darker than the rest of the cell. 



Serosae from somewhat older embryos, while giving no sure signs of 

 degeneration, have nuclei slightly different from those of the youngest 

 membranes. The amount of chromatic substance appears to be larger. 

 It is gathered into denser and more deeply staining masses, and the 

 nucleoli become larger and more stainable (compare Figures 4 and 5, the 

 former from an older membrane than the latter). Many nuclei at this 

 stage become irregular in outline, and are more or less shrunken in 

 appearance, changes which prepare the way for complete degeneration, 

 found in membranes from the oldest embryos. The nucleus here 

 becomes shrunken into a formless mass, which stains deeply and uni- 

 formly. This condition seems to be due almost wholly to loss of the 

 karyoplasm, for the nuclear membrane is seen to be drawn closely 

 over the much condensed chromatic substance. The uniformly staining 

 effect, however, is generally believed to be produced by the solution of 

 a part of the chromatin in the karyoplasm ; this is best seen in nuclei 

 that have not completely degenerated, where the deeply stainable solid 

 chromatin is immersed in the less stainable matrix. Not all the nuclei 

 in a membrane are affected to the same degree by the degenerative 

 change. This is shown in Figure 14, where the nuclei of cell a, and that 

 of the cell farthest to the left, are more affected than any others. But 

 in the oldest membranes almost every nucleus has undergone extreme 

 degeneration. 



