198 ON VARIABILITY AND ADAPTATION 



the form of nucleoli at the periphery immediately beneath the 

 nuclear membrane. These nucleoli are usually spherical, and 

 vary somewhat in size. At this stage yolk granules are absent 

 from the cell. With an indigo carmine dye he found that the 

 nucleus and cell body stained red, whereas the nuclear bodies 

 took on a deep blue. At what appeared to be clearly a later 

 stage, yolk spherules made their appearance, and when this 

 happened the whole ovum stained blue, the nuclei being dimin- 

 ished in size. What appeared to be an intermediate stage was 

 seen in ova in which the nucleoli and the cell substance in their 

 immediate neighbourhood exhibited a blue stain, while the rest 

 of the nucleus and the main mass of the cytoplasm still stained 

 red. It was difficult from these observations to arrive at any 

 other conclusion than that the nuclear matter becomes differ- 

 entiated into nucleolar, and that this diffuses gradually through 

 the nucleus and then into the cell substance, the diffusion coin- 

 ciding in point of time with the formation of the yolk granules. 

 Macallum thus regarded the yolk granules as formed by the 

 union of a derivative of the nuclear chromatin with a constituent 

 of the cell protoplasm. And we here note that these yolk granules 

 chemically are composed in the main of lipoid material, of 

 lecithin, a compound to which I shall refer later. In the pan- 

 creatic cells Macallum found and Steinhaus has made similar 

 observations that the nuclei possess safranophilous nucleoli, 

 while the rest of the nucleus with double staining takes on a 

 deeper red colour of haematoxylin. As the nucleus loses its 

 safranophilous substance, the cell protoplasm acquires safrano- 

 philous granules. He concluded that the chromatin of the 

 nucleus gives rise to a substance prozymogen ; sometimes it is 

 dissolved in the nuclear substance, sometimes collected in masses 

 (plasmosomes) ; finally it diffuses out into the cell protoplasm, 

 there meeting with a constituent of the latter to form the zymogen 

 proper. 



I might proceed to detail a long series of confirmatory obser- 

 vations by Carlier, by Bensley made here in Toronto by 

 Maximow, Solger, Nicholas, E. Miiller, Krause, Galeotti, Vigier, 

 Gamier, Greenough, and others, all agreeing save in minor 

 details and all bearing upon the processes seen in gland cells. 

 All describe the smallest and first seen granules as situated in the 

 immediate neighbourhood of the nucleus; described these as 



