92 



BIOLOGICAL LECTURES. 



'<m. 



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 {in). 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 

 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 ciHary 



motion. This stimulus may be a me- 

 chanical one, as, for instance, granules 



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



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



Fig. 4. 



Fig. 5. 



