Page:Proceedings of the Royal Society of London Vol 60.djvu/53

Rh short, granular colls are formed during larval life by modification of ciliated cells, the interm ediate cells being a stage in this process.

Sections of larvae confirm and amplify the results obtained from a study of the living object (fig. 8). The inner portion of each ciliated cell, which in life appeared refractile, is seen to contain a series of vacuole-like structures, containing granular masses suspended in their interior. A t the junction between the internal vacuolated and external granular portions of the cell is situated the opaque and deeply staining nucleus, which has a form like an onion, and is continued externally into the flagellum. Often the inner side of the nucleus is indented by the vacuole beneath it, sometimes to such an extent th at the nucleus has the form of a crescent in section. The interm ediate cells are very distinct in sections, and by some methods of preservation and staining, e.gr., osmic acid followed by picrocarmine, their protoplasm takes up the stain in a rem arkable manner, so that larvae treated in this way appear to have a brightly coloured equatorial zone. They lack the vacuolated inner portion, characteristic of the