Nachdruck verboten. 

 Uebersetzungsrecht vorbehalten. 



The History of a Transient Nervous Apparatus 

 in certain Ichthyopsida. 



An Account of the development and degeneration of ganglion-cells 



and nerve-fibres, 



By 



John Beard, D. Sc, 



University Lecturer in Comparative Embryology and in Vertebrate 

 Zoology, University of Edinburgh. 



Fart I. Baja batis. 



With Plates 22—29. 



Contents. 



Introduction. 

 Historical. 



Prefatory remarks on observations. 



Description of the transient nervous apparatus in a progressive 

 series of Raja embryos. 



A. The development etc. of the apparatus. 



1. Embryos of 5 — 11 mm. 



2. „ „ 12-13 „ 



3. „ „ 17—20 „ 



4. „ „ 21—25 „ 



5. „ „ do oi „ 



6. „ „ 42-45 „ 



7. „ „ 53 — 60 „ 



8. Embryo „71 mm — critical stage. 



B. The degeneration of the transient nervous apparatus. 



9. Embryo of 8,7 cm. 



10. „ „ 10,5 „ 



11. n r, 12,5 „ 



!*• « n 14 ,, 



