THE BEGINNINGS OF LIFE. 185 



the spores which ultimately appear. Lighter coloured 

 areas are then produced around these nuclei 



believe that the nuclei of many cells in the human body, and in animals 

 generally, are not unfrequenfcly produced after this fashion. The appear- 

 ances in Hydrodictyon are thus described by Braun (loc. cit. p. 261), 

 ' At the time when gonidia are about to form, the mucilaginous contents 

 of the cells change altogether in appearance. The fresh transparent 

 green becomes more opaque, and the entire mucilaginous layer acquires, 

 even before the solution of the starch granules is completed, a peculiar 

 regular appearance, closely beset with lighter spots, which appearance, 

 however, is only distinctly perceptible when the focus is adjusted to the 

 bottom of the mucilaginous layer. These spots are not the starch 

 grains undergoing solution, as might be conjectured, for their number is 

 much larger than that of the latter. . . . The little green granules of the 

 contents, which, for the sake of brevity, I shall call chlorophyll granules, 

 do not disappear with the starch grains, but separate from each other as 

 the period of the formation of the spots, and become accumulated as 

 dark boundary lines between the brighter spots. . . . The spots themselves 

 are roundish spaces free from granules existing in the thickness of the 

 mucilaginous layer.' A little further on (p. 266) Braun says : 

 ' Seeking, in the first place, the import of the light spots which charac- 

 terize the first stage of the new cell-formation of the water-net, it is 

 beyond doubt that they represent the centres of so many new cells, con- 

 sequently are either actual nuclei, or, since we cannot detect any defined 

 outlines, accumulations of albuminous substance analogous to nuclei.' 

 This mode of formation of nuclei was also fully recognised by Naegeli. 

 He summed up his researches on the subject in the following manner : 

 ' The nucleus originates in two ways ; either free in the contents of 

 the cell or by division of a parent nucleus ' (Henfrey's Translations, Ray 

 Society Pub. 1849, P- l68 )- Tn nucleus is described as appearing in 

 the embryo-sacs of Scilla cernua and other flowering plants in the form 

 of * globular drops of perfectly homogeneous mucilage.' The nuclei in 

 the large ventral glands of some of the Free Nematoids, and in the 

 glandular substance lining the longitudinal muscles of others, present 

 precisely similar characters, and may be seen represented elsewhere 

 (Phil. Trans. 1866, PI. 27, fig. 8, and PI. 28, fig. 32 c.), in a memoir 

 on the anatomy of these animals. Whilst still unaware of the views 

 above mentioned concerning the origin of the nucleus I had come to 



