364 JOHN BEAED, 



groups in the mesoderm. The simple spun fibrils of earlier stages are 

 now but rarely met with, the nerves of the system have become more 

 complicated. Sub-epiblastic nerves attain a high degree of develop- 

 ment. In short, taking all its characters into consideration, the 

 transient apparatus of ganglion-cells and nerves has reached its cul- 

 mination-point. This it will retain for a short span of time — "drest 

 in a little brief authority" — and then the long slow process of de- 

 generation will be initiated ^). 



With the commencement of the ganglion-cells in the branchial 

 region, as defined above, their number is not large: over a great 

 many sections they occur in ones and twos, presenting nothing worthy 

 of special remark. Still further back, just in front of the heart and 

 then beyond it, the cells become far more numerous. 



The central cells, provided with capsule-cells, are still as vigorous 

 and thriving as in previous stages (Figs. 40 and 102). The cell body 

 is plump and the nerve-processes are as strongly developed as of 

 yore. The nucleus and its contents furnish as yet no evidences of 

 degeneration. In addition to the central cells, and those found here 

 and there in the mesoderm, ganglion-cells, embedded in the muscle- 

 substance of the myotome, are pretty frequently encountered. Two of 

 these from embryo No. 229 are depicted in Fig. 64, plate 25 {gl.c^). 

 Such cells no longer appear to be in connection with nerves in any of 

 the instances seen — a circumstance accounted for perhaps by the 

 obvious degenerative characters which they present. Their outlines 

 are somewhat irregular, and with carmine stains the cell-body takes 

 on a dull yellowish-brown colouration. No processes can be made out, 

 and, in some instances, degeneration appears to have gone forwards 

 so rapidly that a nucleus is not apparent (Fig. 59, pi. 25 gl. c^). When 

 the nucleus can be resolved, one or more unhealthy-looking nucleoli 

 are also in evidence. 



These cells are by no means rare in embryo No. 229, in others 

 of about the same size, and in older ones. Often they crop-up in 

 twos and threes in a single section. 



A curious group of possibly degenerated, "lost and strayed" 

 elements of the transient system is indicated by the numeral 3 in 

 Fig. 58, plate 25, in the immediate neighbourhood of the lateralis 

 nerve. 



1) The process is far slower in Baja than in some other forms, 

 where the months of the proceeding in Raja are represented by days. 



