of the Fishery Board for Scotland. 



73 



VIII. — A DESCRIPTION OF THE ADVANCED EMBRYONIC 

 STAGE OF LAMNA GORNUBIGA. By Edward W. Shann, 

 B.Sc, Gatty Marine Laboratory, St. Andrews. 



(Plate IX.) 



Introductory. 



Two well-advanced embryos of Lamna comubica— the common porbeagle 

 — together with the entire, oviduct of the mother, were presented to the 

 Zoology Department of St. Andrews University by Dr. H. C. Williamson, 

 M.A., F.R.S.E, Professor M'Intosh kindly offered me the interesting task of 

 describing this valuable material. While engaged upon preparing the notes 

 for publication, the writer was fortunate in meeting Mr. H. Bolton, Curator of 

 the Museum at Bristol, who offered for dissection another embryo of Lamna, 

 which he had received from Dr. Williamson about three months previously. 

 The Bristol specimen furnished not only a useful check on the observa- 

 tions made at St. Andrews, but, owing to slight structural differences, 

 a clue to the manner of development. The fact that the latter specimen was 

 examined at York will be used in distinguishing it from those which were 

 examined at St. Andrews. 



Before proceeding to the account of the work done, the writer wishes to 

 express his gratitude to Professor M'Intosh, Dr. H. C. Williamson, Mr. H. 

 Bolton, and Mr. James Ritchie for the use of material, and for answering 

 patiently his numerous questions. 



General Remarks. 



The only literature on the subject which was forthcoming consisted of a 

 short paper entitled "Notes on an Intrauterine Specimen of the Porbeagle 

 (Lamna comubica)" by W. L. Calderwood.* This contained an account of 

 the external features of a single embryo, measuring 10| inches, which was 

 obtained from the uterus (oviduct) of an adult female at Aberdeen ; un- 

 fortunately, Mr. Calderwood's drawings of this specimen were not published. 

 Pennantt mentions a porbeagle which " had in its belly four young ones, 

 each eight and twenty or thirty inches long." In a letter from Dr. Williamson, 

 several instances of the occurrence of porbeagle embryos are mentioned, 

 viz.: — "I sent one, obtained 29th March 1909, to the Scottish Museum. I 

 " am under the impression that other specimens are there. Two specimens 

 " are in the Laboratory here, but neither has a date. Mr. Ingram, Fishery 

 "Officer, Leith, says that, so far as he can recollect, a female shark having 

 " twins was obtained in a herring-net at Stornoway probably about June. 

 " One large embryo of the porbeagle was sent by Mr. Ingram from Stornoway 

 " to the Fishery Board's Laboratory. It is the largest I have observed. 

 "The embryo is 19 inches in total length, and the yolk is very large, the 

 "yolk-sac measuring 9^ inches in length. The adult from which Mr. 

 " Ingram obtained the twins was about five feet long." The embryos at St. 

 Andrews measured 24 and 18 inches respectively in total length; the adult 

 from which they were obtained measured about five feet. The specimen at 



* Sixth Annual Report of the Fishery Board for Scotland, p. 263, 1887. 

 tBrit. Zool., Vol. III., p. 118. 



