568 DKS, GEOKaE AND FRANCES E. HOGGAN ON 



parallel throughout. In such sections it is difficult to distinguish 

 the central group of fibrils, as they lie parallel with the others and 

 can only be differentiated from them by careful focusing of the 

 microscope. This is necessary also in examining the individual 

 fibres formed by the inner circle, where the focus must be altered 

 to the depth of the diameter of the column under a high power. 

 Eor the same reason, in drawing these fibres it is necessary to 

 limit them to those forming one half of the circle, as shown in 

 our fig. 1, Plate XIII. ; otherwise they would appear so closely 

 packed and mixed up together, that it would be impossible to dis- 

 tinguish the individual fibres in the drawing. Careful examina- 

 tion of the fibres of the inner circle show that they lie outside of 

 a cylinder or column of epidermic cells, as shown in fig. 8, Plate 

 XIII., which is a drawing of a transverse section of the organ at 

 the level of the lower surface of the epidermis. These epidermic 

 cells are built up with great regularity; and at the intervals between 

 the cells each fibril shows a swelling at the same level (see fig. 2) ; 

 and this swelling, although only slightly marked at the lower por- 

 tion of the fibril or organ, becomes developed into distinct buds con- 

 nected by a short pedicle to the fibril as the latter approaches the 

 free surface ; and as these buds lie all at the same level, they give 

 a striated appeal ance to the inner circle or column of fibres when 

 seen under a low power. On reaching the corneal layer of the free 

 surface of the epidermis, the fibrils break into small portions, each 

 containing a bud, which, when it reaches the free surface, is thrown 

 off like the superficial cells of the epidermis. Upon this peculiarity 

 an imjDortant hypothesis has been developed by Professor Eanvier, 

 to which we shall afterwards call attention (p]3. 576 and 586), 

 for the purpose of showing its inapplicability. Between these 

 fibrils and those belonging to the outer circle there is a peculiar 

 distinction of great value in deciding their real character, which 

 has not only passed unnoticed hitherto by previous observers, 

 but has not even been drawn in any of the numerous drawings 

 hitherto published. That peculiarity consists in the fact that at 

 the lower portion of the organ the inner fibrils have a consider- 

 able thickness, and that each fibre tapers off to a mere line as it 

 passes towards the free surface of the epidermis. In the fibres 

 of the outer circle, it will be seen that they are as a rule quite as 

 narrow and fine at the lower as at the upper surface of the epi- 

 dermis. It will also be noticed that these outer fibrils, like the 

 centre ones, have a more or less zigzag course, while the fibrils of 



