368 JOHN BEARD, 



at any rate that of most of them. Some few, as in other parts of 

 the body also, may persist, as will be described at a later period. 

 The point has been referred to at this juncture simply because 

 sections of the tail of embryo No. 237 were available, and one such 

 has been figured in Fig. 77 of plate 26. The large ganglion-cell lies 

 in the usual position near the summit of the cord. Its multipolar 

 nature is recognisable but — and this is very characteristic of these 

 cells in the tail in this and even in earlier stages — it appears to 

 be already in process of degeneration. A similar cell from near the 

 tail end of an older embryo (No. 255, 71 mm) is sketched in Fig. 77 a 

 of the same plate, and three such cells from the spinal cord of the 

 tail of the same embryo are to be seen in Fig. 78. These latter 

 appear to have undergone some degeneration. With haemotoxylin 

 these cells have taken on a yellowish-brown colouration, their outlines 

 are somewhat irregular and their boundaries (Umrisse) somewhat sharp. 



7. Embryos of 53— 60 mm. 



Under this heading there will firstly be described an embryo 

 (No. 345) of 54 mm. The external gills of this embryo are remark- 

 ably short, i. e. 4 — 5 mm. The unpaired caudal fins are well defined. 

 Its sex is not yet externally obvious. From head to pelvis it measures 

 16,5 mm, the rest of its length belonging to the tail. 



Figs. 103 (plate 28) and 114 (plate 29) are intended to demonstrate 

 the condition of the centrally lying cells of this embryo. They are 

 still healthy and provided with capsule-cells. The nucleus is large 

 and filled with granular contents, including highly retractile nucleoli. 

 Transient nerves, as in embryo No. 229, can still be detected. Al- 

 together, the condition of the transient system in this embryo exhibits 

 neither advance nor any very marked retrogression from that of embryo 

 No. 229. Ganglion-cells are as frequently met with in the mesoderm, 

 and also in the myotome. Some, at any rate, of those in the meso- 

 derm have their axis - cylinders, which brought them in touch with 

 central cells, shrunk and withered. 



On plate 23, Fig. 34, a ganglion-cell (w.gl.c) at the end of a 

 transient nerve, lying near the lateral line (U) and the myotome 

 (m.p), is drawn from the present embryo. It and its nerve-process 

 appear both to be in a healthy condition. This figure recalls in a 

 striking manner Figs. 58 and 61, plate 25, which, it will be remem- 

 bered, were found in embryo No. 229. 



