358 JOHN BEARD, 



Figs. 50 pi. 24 and 69 pi. 25 are taken. In this embryo the lens and 

 retina are more developed than in No. 192, and the lateral line 

 extends further back. Fig. 50, plate 24, shows three transient cells 

 in the cord, one of which sends ofl a long axis-cylinder process (w.p) 

 along the outer side of the myotome. Apart from the differences 

 brought about by another mode of preservation, this embryo shows 

 much the same as the preceding one. As in it sub-epiblastic nerves 

 are not a marked feature. These conclusions may be gathered from 

 a long analysis in my note book — an analysis which need not be 

 transferred to this paper. 



Fig. 69, pi. 25 may be briefly mentioned at this stage. It depicts a 

 large, apparently degenerate, cell (d.c) lying near the ventral portion 

 of the central canal of the cord. It is filled with large particles, of 

 a fatty or yolk nature, probably fatty, blackened with osmic acid. 

 Similar structures have been encountered in several other embryos, 

 more especially in very young embryos, but also, as in this instance, 

 in embryos in which yolk may no longer be expected to occur in the 

 cells. Such cells are always of large size, they are also met with in 

 embryos in which osmic acid did not form a factor in the preserving 

 fluid, and they put in an appearance in very varied regions. Thus 

 in early stages they are met with in and among the various layers, 

 sometimes in the somatopleure, or in the splanchnopleure, and even 

 in the fore-brain as in Fig. 70. 



Passing now to embryos of 25 mm, the general characters of three 

 (Nos. 201, 202, 203), of about the same age, will be briefly defined. 

 Forked muscle-buds from about 46 somites on each side are present 

 in the paired fins. The first traces of the two unpaired caudal fins 

 are apparent, but as yet these are unprovided with muscle buds. The 

 external gills on the two posterior arches are very short, larger on 

 the other three. The neurenteric canal no longer exists. In these 

 three embryos the lateral line thickening extends for about 3 mm 

 posterior to the auditory capsule, and ceases near the anterior ends 

 of the paired fins. From these embryos figures of one horizontal 

 section (Fig. 73) and of three transverse sections (Figs. 46, 47 and 86) 

 will be explained. 



Figs. 46 and 47, pi. 24, from embryo No. 201, may be referred to as 

 showing the condition of the centrally-lying transient ganglion- cells 

 at this stage. They are still plump and well-nourished, with granular 

 protoplasm, a large nucleus with granular contents and several highly 

 refractive nucleoli. Capsule-cells (c. c) closely embrace each ganglion-cell 



