92 BIOLOGICAL LECTURES. 



blue with haematoxylin, and which are arranged in regular rows. 

 On the outer end of these minute rods (b) (which I have called 

 basal rods) are attached small round masses of 

 a light blue staining substance (m). All these 

 latter masses are in contact with each other, and 

 it seems to me that this is the most important 

 detail in the whole structure. From the outer 

 ends of these round masses, or, as we might 

 f call them, middle pieces, arise the true flagella 



(/), the long thin cilia. Thus a cilium consists 

 of three parts, the basal rod, the middle piece, 

 and the flagellum (Fig. 4). So much for the 

 structure of the cilium proper. 



The structure of the cell to which these cilia 

 belong is none the less remarkable. We know 

 that in ordinary cells the cytoplasm consists of 

 two distinct substances : a fibrillar substance, 

 which forms a fine threadwork with innumerable 

 meshes, and a fluid which lies between these 

 meshes. In the ciliated cell the fibrillar sub- 

 stance is distributed in a very regular way. 

 There are no meshes to be seen, but 

 all the fibres run parallel to each other 

 and at right angles to the ciliated sur- 

 face, clear through the whole width of 

 the cell. There are no anastomoses 

 between the fibres (cp). They show no 

 relation to the nucleus. On the inner 

 side of the ciliated surface and also 

 around the nucleus we find a great 

 number of fine pale granules (Fig. 5). 

 Now to our theory. I believe that 

 a stimulus coming from the exterior 

 is necessary to produce the ciliary 

 motion. This stimulus may be a me- 

 chanical one, as, for instance, granules FlG - s- 

 striking the ends of the flagella ; or, still more probably, a 

 chemical one, for instance, oxygen in statu nascendi, which we 



