374 JOHN BEARD, 



Sections from two embryos of this size have been available, from 

 one only, No. 294, the following figures have been taken: — Fig. 113 

 and 113a, plate 28, Figs. 117, 118 and 125, plate 29. 



In Fig. 113 and 113 a the transient ganglion-cells are firmly 

 wedged into the posterior fissure of the cord. They are much elon- 

 gated, and practically nothing can be made out as to the remains of 

 their processes. Changes have undoubtedly gone on within the nucleus, 

 for the nucleoli no longer have the same appearances as formerly. 

 This is perhaps better seen in Figs. 117 and 118 of plate 29. Each 

 of these figures depicts transient ganglion-cells — under higher magni- 

 fication — from the anterior part of the cord, a region where they 

 are not so pressed down into the fissure. The nucleoli of these cells 

 appear to be more swollen-up, and perhaps turgid with fluid contents. 

 There seems to be also a breaking-up in the general structure of the 

 nucleus, an attempt to depict which has been made in Fig. 118. 

 Figs, 117 and 118 also exhibit the shrunken and shrivelled remains 

 of some of the processes. 



Fig. 125 is of interest, because it reveals a much degenerated 

 ganglion-cell lying encapsuled in the mesoderm near the myotome. 

 This cell has degenerated far more rapidly than its centrally-lying 

 fellows, so rapidly that little remains of it or of its nucleus. The 

 interesting fact about it, however, is that in getting less and less it 

 has shrunk away from the walls of the capsule in which it was en- 

 tombed, and in such a way as to reveal the original size of the cavity 

 which it formerly filled. It is now a mere shapeless bit of proto- 

 plasm with the withered remains of a nucleus. 



13. Embryo of upwards of 16 cm. 

 The total length of embryo No. 315 is rather more than 16 cm. 

 From the tip of the rostrum to the end of the pelvic fins measures 

 6,5 cm, the rest belongs to the tail. Across the widest part of the 

 pectoral fins from side to side is 7,25 cm. There are no traces of 

 external gills visible. The embryo is 11 — 12 months old. On plate 29 

 are three figures from this embryo (Figs. 119 — 121). The first of 

 these is a drawing under high magnification. The very greatly withered 

 processes (n.p) of the cells are seen , but in this embryo the cells 

 themselves, though tending to become shapeless (Fig. 121), are not 

 so compressed as in some of the figures previously described. As 

 shown in Fig. 119, the outlines of the nuclear membrane tend to be- 

 come irregular, and the nuclear contents show a further advance in 



