THE EARLY DEVELOPMENT OE THE MAESUPL\LIA. 53 



cells are more variable in size, the nuclei thus appearing less 

 uniformly and less closely arranged, and they stain, on the 

 whole, somewhat less deeply than those of the lowei- hemi- 

 sphere. The non-formative cells are on the average smaller 

 than the largest of the formative cells, but they are more 

 uuit'orm in size, and their nuclei thus lie at more regular 

 distances apart, and appear more closely packed. They are 

 also richer iu deutoplasmic material, and so stain rather more 

 deeply than the formative ceils. Sections show that the 

 cellular wall is unilaminar throughout its extent, and that, 

 whilst it is somewhat thicker than that of So mm. vesicles, 

 it is still very attenuated, its thickness, including the shell- 

 membrane, ranging from '00-4 to "008 mm. I have examined 

 a number of series of sections taken through portions of the 

 wall known to include the sutural line, and find it quite 

 impossible to locate the position of the latter; indeed, I 

 cannot certainly distinguish betAveen the formative and non- 

 formative regions. 



In the blastocyst cavity,, lying' in contact with the inner 

 surface of the wall, and most abundant in the region of the 

 formative hemisphere, there are present numbers of deeply 

 staining spherical cells with relatively small nuclei similar to 

 those described in connection with the o"25 mm. vesicles. 

 They occur singly or in groups, and may appear quite normal 

 or may show more or less evident signs of degeneration. 

 Their nuclei may stain deeply and homogeneously, or may be 

 represented by one or two deeply staining granules, vacuoles 

 may occur in their cytoplasm, and spherical cytoplasmic masses 

 of very variable .size, with or without deeply staining granules 

 of chromatin, may occur along with them. In sections and 

 preparations of the wall of these and other 4*5 mm. vesicles 

 there are to be found, in both the formative and non-formative 

 hemispheres, small localised areas from which such spherical 

 cells are being proliferated off in numbers together. PL 5, 

 fig. 47, from the formative hemisphere of an ^04 vesicle shows 

 one of the most marked examples of such proliferative activity 

 that I have encountered. A similar but smaller proliferative 



