76 



Part III. — Twenty -eighth Annuo! Report 



The presence or absence of spiracles in Lamna cornuldca is still an open 

 question. Sir William Turner* describes minutely the spiracles in a young 

 female measuring o\ feet, but these were only wide enough to admit the 

 passage of a pig's bristle. Spiracles are also said to be present by MUller 

 and Henle, in their work on the Plagiostomala, by Yarrell in his ''British 

 Fishes," and by Dumeril in his '-Hist. Nat. des Poissons." Fleming, Couch, 

 and Parnell state that they are wanting. Day compromises with the remark. 

 u Spiracles, if present, minute;" Tate Regan, in his "Classification of the 

 Selachian Fishes," agrees with this conclusion. Giinther found no spiracles 

 in L. cornubica, but states that "a minute pore-like foramen could be seen 

 "on one side of an example of L. spallanzani." Mr. W. L. Calderwood,* 

 in describing bis embryo porbeagle, says : — " In this young specimen the 

 " skin between the eye and gill slits was very soft and much wrinkled, and 

 " although examined carefully with a lens revealed no aperture." The 

 result of a similar examination of the specimens at St. Andrews corroborated 

 this statement ; in the specimen at York, however, a small pit was observed 

 on either side of the head, level with the centre of the eye, and in each case 

 22-5 mm. from the margin of the latter. The position agrees well with thai 

 observed by Sir W. Turner,t but some doubt remains whether these were 

 actually the openings of spiracular canals or merely surface pits. They 

 would not admit the passage of a hair ; and when a fine surgical wire was 

 used, it was found that the wire did not follow a definite channel, but 

 forged a course for itself through the soft vacuolated tissues. The tissues 

 were unfortunately too soft for sectioning, or some evidence might have 

 been obtained in this manner. Careful examination did not reveal an 

 internal spiracular aperture in the pharynx. 



The minute spiracles which have been found in adult porbeagles by 

 various observers can be of very little use to the fish ; if they were of vital 

 importance they would be present invariably. It is probable, then, that the 

 spiracles of Lamna cornubica are abortive structures. By the law of re- 

 capitulation, the spiracle is formed in the embryo, but disappears in most 

 cases before, or soon after, birth. This interpretation of the facts is only an 

 hypothesis, and must await further investigations. 



The five gill slits were opeu and the gills fully developed. All the fins 

 were normal with the exception of the caudal, whose dorsal and ventral lobes 

 had not yet expanded, but had a chelate appearance. The keel on the sides 

 of the posterior end of the body, also the notch in the back at the base of 

 the caudal fin, were characteristic. The skin was slightly roughened with 

 developing scales (Plate IX., fig. 2). The colouring of the trunk and fins was 

 normal ; the yolk-sac was yellow. The cloaca was open. 



Owing to the courtesy of Mr. James Ritchie, M.A., B.Sc, the writer was 

 enabled to examine the porbeagle embryo which was sent by Dr. Williamson 

 to the Royal Scottish Museum. This form was a female measuring 

 21 1 inches in total length, and the yolk-sac was still of enormous bulk. 

 The young fish was slightly better developed than those examined at St. 

 Andrews. The inter-nasal groove had almost disappeared, the teeth were 

 numerous, and the chin-pit was almost filled out, being only represented by 

 two grooves which ran from the first gill slit towards the point where the 

 pit was formerly placed. In this example, too, a pair of minute pits were 

 observed an inch behind the margin of the eye, one on each side of the head. 

 It was not clear whether the pits communicated with an internal passage. 

 It was not possible to effect an entry with a hair or waxed thread. This is a 

 similar condition to that recorded above for specimen C, and seems to render 

 it yet more probable that these pits have some connection with tha proble- 

 matical spiracles. 



* Journ. Anat. and Phys., 1875, p. 301. 

 t Op. cit. 



t I did not see the ulterior, but there were no traces of claspers. 



