394 JOHN BEARD, 



nearly a year and half! Nothing more would have been gained from 

 later stages. Besides, as all the transient ganglion-cells do not atrophy 

 with equal rapidity, further search in the later embryos would have dis- 

 closed traces of cells in an even more withered and decayed condition 

 than those of Fig. 131. That such have not been figured may be set 

 down to the inclination of the embryologist to pick out the best of them 

 for delineation. If, as often happened, the final stages of a cell met 

 the eye, such were rejected as revealing nothing worth drawing. 



But even in Fig. 131 the cells are contorted and withered beyond 

 recognition, and, therefore, it is not too much to say that for Baja 

 the demonstration of the degeneration is complete, and that thus the 

 transient nature of the ganglion-cells, nay, of the nervous apparatus 

 as a whole, is established. 



General remarks on the formation of nerve in the transient 



apparatus of Raja. 



The formation of many of the transient nerves of Raja affords 

 irrefragable evidence of the truth of the statement that nerves may 

 be formed and that some nerves do arise as processes of ganglion- 

 cells. But if there be an undoubted instance of the formation 

 of a nerve by cell-chains , whether ganglionic or not , it of course 

 follows that there are exceptions to the rule, and that one may not 

 generalise the statement into an assertion that all nerves arise as 

 processes of ganglion-cells. One exception is that figured for both 

 sides of the body in Fig. 24. There are, indeed, others which may 

 belong to the same category, such, for instance, as the nerves of 

 Figs. 7, 8, 9 and 88. Here, however, owing to some complexity in 

 the composition of the nerves it is not possible to say more of them 

 than that each is a plexus of nerve-fibres and ganglion-cells. 



On my own part there exists a desire to postpone consideration 

 of the "process" and "cell-chain" theories of nerve-origin until a later 

 stage of the investigations; but there is always the possibility, or 

 probability, of citation by others of the facts here recorded, and hence 

 the wish arises to avoid any misunderstandings on the matter. 



Even granted that all the nerves of the transient system arose 

 as processes of cells, there would remain a long array of other obser- 

 vations, as yet not published, on other nerves of Raja^ which so far 

 are quite inexplicable on the "process" view. The mode of formation 

 of twigs of the spinal nerves of Raja^ for instance, is absolutely in 

 favour of the "cell-chain" theory. 



