History of a transient nervous apparatus in certain Ichthyopsida. 337 



section much further back, it is difficult to distinguish between those 

 cells of the roof which belong to the future spinal ganglia and those 

 which are to become transitory ganglion-cells. On the one side only 

 is there a cell (sp.c), with long process, like many of those just de- 

 scribed, which is unquestionably nerve-forming. On this process are 

 two nuclei, but these to not appear to belong to this developing axis- 

 cylinder. From this and other instances in the series under review 

 the conclusion appears warranted that cells (nerve- forming ones) may 

 spin or form nerve-processes before they have acquired ganglionic 

 characters — if they ever are to become ganglion-cells at all! ^) And 

 this is a conclusion to which one is forced time after time in study- 

 ing the development of this transient nervous apparatus. There still 

 remain to be described some very interesting and important figures 

 from this remarkable series, — figures which reveal in great perfec- 

 tion the characters and course of the sub-epiblastic nerves of the 

 system. 



Figs. 1 and 2 of a former paper (No. 3) were both taken from 

 the embryo under consideration. There now follows the description 

 of three sections, figured in Figs. 7, 8 and 9, of which the drawings, 

 if combined, would give some such figure as fig. 2 of the preliminary 

 paper. In the present instance it has been thought best to give 

 camera-drawings of the three consecutive sections without combination 

 of them, leaving this to the reader to make for himself. In other 

 cases, to be recorded later on, combined drawings are ofifered. It is 

 impossible to faithfully render the details of shade and colour in the 

 sketches. The ganglion-cells, both those at the centre and those along 

 the courses of the nerves, are of a delicate pale pink colour, nerve 

 and protoplasm are yellowish-brown, the cells of the rest of section 

 of the usual carmine red ^). The three figures, however, fulfil a mor- 

 phological rather than a histological purpose. Taking the three to- 

 gether they reveal the origin and course of two — ? a pair of — nerves 

 of the transient system. These nerves are not of the simple fibrillar 

 nature of some to be described in other embryos. They are rather 



1) Compare the section on "degeneration of ganglion-cells". 



2) Like many others of the collection this embryo was treated 

 with Rabl's picric-platinum-chloride mixture and stained with — borax- 

 carmine ! I have treated embryos in all sorts of ways, to appease, by 

 anticipation, various critics of methods, but have been best satisfied 

 with those methods which revealed most — even when they were 

 simple and "antiquated" in nature. 



