74 



Part III. — Twenty-eighth Annual Report 



York was 18J inches long.* R. Collet t lias measured various specimens of 

 the porbeagle embryo from the Museums of Christiania and Trondhjem ; he 

 speaks of them as half-grown or rather more than half-grown. The adults 

 which contained these embryos were taken on cod and halibut lines during 

 the winter months. The following is a list of the embryos examined by 

 Collet :— 



"Selje, Nordfjord, 30th Dec. 1892; 1 embryo, 290 mm. 



" Lyngen, W. Finmark, 1st Jan. 1891 ; 2 embryos, 295 mm. 



; 'Rovaer, Stavangerfjord, 21st Feb. 1888; 4 embryos, 425 mm. (17 ins.). 



" The adult containing the latter measured 2565 mm. (nearly 8£ feet). 

 " The yolk-sac of the embryos had still a diameter of 185 mm. The 

 " pectorals were 47 mm., the upper lobe of the caudal fin 121 mm., and 

 "the lower 54 mm. in length. J These embryos would probably have been 

 " born in April or May. 



" A specimen (2800 mm., or over 9 feet) caught off the inner islands on 

 ' ; 15th February 1905 contained three large embryos." 



It is difficult to believe the report in the Memoirs of the Wernerian 

 Society which states that "no fewer than thirty young ones appeared in the 

 u belly of this female, fully formed and apparently ready for exclusion." 

 This is the only record, aniDng those examined, which gave more than four 

 as the number of young at a birth for the porbeagle. Dr. Williamson 

 says, " I do not know of any adult porbeagle having more than three young 

 at a time." Two young at a birth is apparently the most frequent number, 

 one being found in each oviduct. 



An argument adduced by Mr. W. L. Calderwood§ may be quoted here: — 



"The figure of the porbeagle given in Day's 'British Fishes' is taken from 

 " a specimen only measuring 33 inches, and thus is not larger than those said 

 " to be dissected from the adult by Pennant. It has quite the adult form. 

 " From this, and from the statement of the Wernerian Society's Memoirs, 

 " we may therefore surmise that at birth the young porbeagle has not only 

 " assumed the matured shape of the parent, but has already absorbed all the 

 ' nourishment to be derived from the yolk-sac, which forms a conspicuous 

 " object in the specimen under consideration." 



It would appear, further, that the young porbeagle at birth measures 

 approximately thirty inches. There is probably considerable variation in 

 this respect, if we consider that porbeagle embryos have been observed 

 measuring 10|, 18, and 24 inches respectively, but all apparently at the 

 same stage of development. It seems possible that the intra-uterine 

 development of this shark may be divided into two fairly distinct periods, 

 which may be styled (1) Formative and (2) Protective — the first, or 

 Formative, period comprising the time during which the organs are 

 developed, and terminated when the eyes, mouth, fins, etc., are fully formed, 

 but the yolk-sac is still conspicuous ; the second, or Protective, period 

 during which the organs already formed simply increase in size at the 

 expense of the yolk, and the uterus acts as a protection to the helpless 

 young. This period ends when the yolk is entirely absorbed and the young 

 fish is born in a condition to shift for itself. The duration of these periods 

 is probably variable. 



Detailed Measurements. 



All the embryos examined were apparently females. There was no sign 

 of claspers on their well-developed pelvic fins. No sexual glands were 

 formed, but in the two examples dissected the oviducts were quite patent. 



* Since writing this account I have been informed by Dr. Williamson that this 

 embryo was obtained from the same adult as those which were examined at St, 

 Andrews.— E. W. S. 



t Meddelelser om Norges Fiske, 1 Aarene 1884-1901, p. 77. 



+ Compare with measurements in this memoir. 



§ Op. cit. 



