ORIGIN OF THE TRABECULE OF THE OPTIC NERVE. 485 



epiblastic trabeculae from the sector that I have filled in with 

 nuclei and fibrils; the other part of the drawing only shows 

 the distribution of the nuclei and some of the thicker fibrils. 

 It will also be evident from this drawing that the stellate 

 arrangement of the nuclei and the trabeculee, found in a 

 32 mm. tadpole^ does not persist; it is gradually lost in 

 succeeding stages. 



V. Pigmentation. 



In the earliest stages of the stalk the fibrils of the proto- 

 plasm surrounding each granule of food-yolk^ are pigmented, 

 and can be traced perhaps separately. 



But, when there has been a confluence of probably several 

 of these, through ingrowth of nerve-fibres, it makes the 

 condensed transverse fibrils, seen in sections transverse to 

 the stalk, stand out in bold relief, and, when one has learnt 

 what to look for by means of these sections, allows the con- 

 densed oblique and longitudinal fibrils to be seen, in longi- 

 tudinal sections, without having recourse to special methods 

 of staining. 



But as soon as the increased flow of lymph, that we have 

 ascribed to the enclosure of the subarachnoidal lymph space, 

 takes place throughout the nerve, the trabeculee, excepting 

 sometimes a very short and thickened piece close to the 

 nucleus, become completely depigmented. 



This renders it afterwards veiy difiicult to follow the 

 delicate, oblique and longitudinal fibrils among the nerve- 

 fibres. 



But even in the adult state the amount of pigment which 

 the thickened end of the fibril sometimes contains near its 

 nucleus is sufiicient to catch the eye when the rest of the 

 fibril would easily escape notice. 



I have not thought it necessary to publish drawings of 

 longitudinal sections from stages later than that represented 

 in fig. 14, as there is nothing further to show than a con- 



