320 JOHN BEARD, 



13. Embryo of 16 cm. 



14. „ „ ly „ 



15. „ a month older. 



16. Recently hatched embryos. 



General summary of the development of the apparatus, its pro- 

 bable functions, and fate. 



1. Comparative development of the apparatus in B,. batis. 



a) Development of the ganglion-cells. 



b) Peripheral ganglion-cells of the transient-system, 



c) Relations to spinal ganglion-cells. 



d) Transient nerves of the system. 



e) Build and comparison of the subepiblastic nerves of 



the transient system. 



f) Physiological nature, i. e. functions of the transient 



system of ganglion-cells and nerves. 



2. Degeneration of the transient apparatus. 



a) The nerves. 



b) The peripheral ganglion-cells. 



c) The central cells. 



General remarks on the formation of nerve in the transient ap- 

 paratus of Raja. 



The degradation of ganglion-cells. 



Preliminary remarks on permanent giant ganglion-cells in other 

 forms. 



Degenerate condition of the apparatus in Raja. 



Comparison of the transient nervous system with the permanent one. 



Development by substitution of organisms, or antithetic alternation 



of generations. 

 Abstract. 



Appendices : 



a) Table of sizes, somites etc. of embryos of R. batis. 



b) Comparison of Raja and Pristiurus embryos (after Rabl) 

 as to somites and gill-pouches. 



