EMBIIYOXIC DEVELOPMENT OF THE PORBEAGLK SUARK. 161 



14. The Embryonic Development o£ the Porbeagle Shark, 

 hamaa cornubica. By E. W. Shann, B.Sc, F.Z.S., 

 Biology Master at Oundle School. 



[Received November 13, 1922 : Read February 20, 1923.] 



(Text-figuves 1, 2.) 



Contents. 



Page 



I. Recapituiatiou of Previous Work 161 



II. Record of Material 163 



III. External Features 164 



IV. Internal Structure 107 



V. Physiology of Nutrition 168 



I. Recapitulation. 



In 1910 I investigated the anatomy of the advanced embryonic 

 stage of Lamna cornubica. My results were published in the 

 Twenty-eighth Annual Report of the Fishery Board for Scotland. 

 Himultaneously with this publication there appeaj-ed a much 

 fuller account of the same subject, profusely illustrated, by 

 Lohberger (4). As this author placed an entirely new interpre- 

 tation upon the anatomy of the alimentary canal, as well as upon 

 the mode of embryonic nutrition, I was desirous of repeating 

 my investigations ; I accordingly asked Dr. Williamson of the 

 Scottish Fishery Board, who had supplied my original material, 

 if ever he obtained more embryos of Lamna to give me the 

 opportunity of dissecting them. Cases of the (.apture of Lamna 

 embryos are few and far between, and it was not until 1922 that 

 Dr. Williamson was able to comply with my request. In 

 Febi'uary of this year a female landed at Aberdeen was found to 

 contain four embryos, each measuiing about 35 cm. in total 

 length. These embryos, together with the entire oviducts and 

 ovaries of the mother, were jjlaced at my disposal ; for which I 

 take this opportunity of thanking Dr. Williamson. One of these 

 embryos was a male, which is of interest as being the first 

 recorded case of the capture of a male embryo of Lamna. 



As the result of my investigation of the latest material, I am 

 able to confirm Lohberger's ob.servations almost in their entirety ; 

 and this despite a strong preconceived scepticism regarding the 

 possibility of his view of the nutritive process, a scepticism which 

 was shared by all the zoologists with whom I had discussed the 

 subject. Briefiy, the facts regarding the development of the 

 embryo are as follows : — 



The original yolk-sac is absorbed at a very early period, when 

 the embryo measures about 6 cm. Thenceforward the cardiac 

 portion of the stomach becomes filled with semi-solid matter, 



Proc. Zool. Soc— 1923, Ko. XL 11 



