366 JOHN BEARD, 



ending appears to be "free". Almost always such nerves occur in 

 pairs, but the intervals of their origin are somewhat irregular, and 

 hence it is out of question to think of assigning to them segmental 

 rank. 



In describing Fig. 59 it was stated that other degenerating 

 ganglion- cells were to be found in the myotomes. In addition there 

 are still some met with in this position which exhibit as yet no 

 marks of atrophy. Two of these, from two adjacent rows of sections 

 will be found depicted on plate 27, Figs. 93 and 94 (glc^). Both 

 cells are nearer the outer than the inner layer of the myotome, a 

 fact about the occurrence of such cells which has been established for 

 previous cases. That in Fig. 93 appeared to be unconnected with 

 any other elements of the transient system, while the one in Fig. 94 

 was probably in touch with a transient nerve. 



At this point Fig. 85 on plate 26 may also be briefly re- 

 ferred to. It represents a portion of the epiblast and of a myo- 

 tome, of a R. radiata embryo (No. 236) of 33 mm. As embryos 

 of this species are smaller than corresponding ones of B. hatis 

 at any period of the development, this embryo, in the actual 

 phase of its development, is not far removed from embryo No. 229. 

 In the layer of the myotome next the epiblast, and some distance 

 from its apex, there appear to be four ganglion- cells. Of the nature 

 of the lowest and largest (gl c^) of these there can be no doubt — 

 it is apparently a normal healthy ganglion-cell of the transient system. 

 Regarding the other three (gl. c 2 — 4) one cannot speak with such 

 certainty ; their outlines are somewhat blurred, and — even with the 

 excellent Leitz lens — their nuclei indistinct, far more so than ap- 

 pears to be the case from the figure. 



But there is little doubt to my mind that they are degenerated 

 elements (which have possibly not functioned at all in this embryo), 

 of the transient system. Embryos Nos. 227 and 237, notwithstanding 

 differences in size between them, furnish practically the same ap- 

 pearances in their transient system as No. 229. But in embryo No. 237 

 the central ganglion-cells do not look quite so healthy as in No. 229. 

 As will be pointed out, it is difficult to say, especially for one who 

 is not a pathologist, when general degeneration has actually just set 

 in. So far as an embryologist can judge, the exact period seems to 

 vary slightly in different embryos*). 



1) The morphological period is defined on page 370. 



