VIII. ON THE DEVELOPMENT OF THE SPINAL NERVES IN 

 ELASMOBRANCH FISHES \ 



With Plates 22 and 23. 



IN the course of an inquiry into the development of Elasmo- 

 branch Fishes, my attention has recently been specially directed 

 to the first appearance and early stages of the spinal nerves, 

 and I have been led to results which differ so materially from 

 those of former investigators, that I venture at once to lay 

 them before the Society. I have employed in my investiga- 

 tions embryos of Scy Ilium canicula, Scyllium stellare, Pristiurus, 

 and Torpedo. The embryos of the latter animal, especially 

 those hardened in osmic acid, have proved by far the most 

 favourable for my purpose, though, as will be seen from the 

 sequel, I have been able to confirm the majority of my conclu- 

 sions on embryos of all the above-mentioned genera. 



A great part of my work was done at the Zoological Station 

 founded by Dr Dohrn at Naples ; and I have to thank both 

 Dr Dohrn and Dr Eisig for the uniformly obliging manner 

 in which they have met my requirements for investigation. I 

 have more recently been able to fill up a number of lacunae in 

 my observations by the study of embryos bred in the Brighton 

 Aquarium ; for these I am indebted to the liberality of Mr Lee 

 and the directors of that institution. 



The first appearance of the Spinal Nerves in Pristiurus. 



In a Pristiurus-embryo, at the time when two visceral 

 clefts become visible from the exterior (though there are as yet 



1 [From the Philosophical Transactions of the Royal Society of London, Vol. 

 CLXVI. Pt. i. Received October 5, Read December 16, 1875.] 



