356 JOHN BEARD, 



45 — 46 muscle buds were counted on each side as passing into the 

 paired fins. No traces of unpaired fins are present. Fig. 56 has 

 already been published as fig. 6 of the preliminary paper (No. 3). 

 It was there described as not an isolated instance of the occurrence 

 of ganglion cells in the regular epithelium of the myotome in Raja, 

 and this statement is abundantly borne out by figures of the present 

 plates. The two cells (gl-c^) here sketched form in fact two members 

 of the outer epithelium of the myotome, and it is possible that they 

 may have developed there. No processes were found connecting them 

 with other elements of the transient system. 



As typical of the general characters of embryos of 21 — 25 mm embryo 

 No. 192 may be described more fully. In this embryo, which measured 

 22 mm when embedded, the neurenteric canal had just closed. The muscle 

 buds to the paired fins are forked, and as yet the unpaired fins give 

 no signs of existence. The lens is a vesicle, quite separated ofi from 

 the epiblast, and its posterior wall has begun to thicken. The same 

 process is also commencing in the retina. On the posterior arches 

 the external gills are very small. Behind the branchial region the 

 oesophagus is solid. The lateral line thickening ceases closely behind 

 the last cleft. In passing, it may be remarked that in embryos of 

 21 — 25 mm the lateral line has an extension varying very much in 

 amount in different embryos; in some it ends just behind the gills, 

 in others it stretches half-way along the trunk. 



The series under review offers no great degree of development 

 of sub-epiblastic nerves, though indications of such are to be seen 

 here and there. A close analysis was made of the sections of this 

 embryo, some of the results of which will be recorded after the 

 description of the five figures relating to No. 192. The figures in 

 question are Figs. 38 and 39, plate 23, Fig. 42 and 43, plate 24, and 

 Fig. 81 on plate 26. In the first of these (Fig. 38) there is a transient 

 ganglion- cell (gLc^) lying in the apex of the myotome, from this cell 

 a long axis-cylinder process (n.p) could be followed nearly into the 

 top of the spinal cord, — it would there end in contact with one or 

 other of the central ganglion-cells shown in the figure. The drawing 

 is a combination from two sections. The following figure (Fig. 39), 

 again composed from two consecutive sections, offers a good example 

 of applied ganglion-cells. There is a certain incompleteness about it, 

 conditioned by the circumstance that the chain of cells and nerves 

 was severed into two portions. Thus arose the break in the con- 



