MEMOIRS. 



A Preliminary Account of the Development of the 

 Elasmobranch Fishes.^ By F. M. Balfour, B.A., 

 Trinity College, Cambridge. (With Plates XIII, XIV, 

 and XV.) 



During the spring of the present year I was studying at 

 the Zoological Station, founded by Dr. Dohrn at Naples, and 

 entirely through its agency was supplied with several 

 hundred eggs of various species of Dog-fish (Selachii) — a far 

 larger number than any naturalist has previously had an 

 opportunity of studying. The majority of the eggs belonged 

 to an oviparous species of Mustelus, but in addition to these I 

 had a considerable number of eggs of two or three species of 

 Scyllium, and some of the Torpedo. Moreover, since my return 

 to England, Professor Huxley has most liberally given me 

 several embryos of Scyllium stellare in a more advanced 

 condition than I ever had at Naples, which have enabled me 

 to fill up some lacunae in my observations. 



On many points my investigations are not yet finished, 

 but I have already made out a number of facts which I 

 venture to believe will add to our knowledge of vertebrate 

 embryology ; and since it is probable that some time will 

 elapse before I am able to give a complete account of my 

 investigations, I have thought it worth while prej)aring a 

 preliminary paper in which I have briefly, but I hope in an 

 intelligible manner, described some of the more interesting 

 points in the development of the Elasmobranchii. The first- 

 named species {Mustelus sp. ? ) was alone used for the early 

 stages, for the later ones I have also employed the other 

 species, whose eggs I have had ; but as far as I have seen at 

 present, the difierences between the various species in early 

 embryonic life are of no importance. 



Without further preface I will pass on to my investiga- 

 tions. 



The Egg-shell. 



In the eggs of all the species of Dog-fishes which I have 

 examined the yolk lies nearest that end of the quadrilateral 



' Read in Section D, at the Meeting of the Britisli A.ssociation at Belfast. 



VOL. XIV. NEW 8ER. Y 



