of the Fishery Board for Scotland. 



77 



Internal Examination of Specimens B and 0. 



Both surfaces of the wall of the yolk-sac were smooth ; the wall was very 

 thin except where it approached the body-wall. The wall was well supplied 

 with blood vessels, whose ramifications could be plainly seen. The yolk 

 formed a dense mass of a pale yellow colour. It was applied closely to the 

 wall of the sac, and found its way into every interstice of the body-cavity, 

 investing completely the abdominal organs. The oesophagus lead into a funnel- 

 shaped organ, whose wide distal end opened freely into the substance of the 

 yolk (Plate IX., fig. 3). The oesophagus was thick-walled, and bore marked 

 longitudinal ridges on its inner surface. The wall of the funnel also showed 

 ridges of thickening at its proximal end, but became thin at the distal end. 

 The margin at the open end was deeply serrated. A lobed mass of tissue was 

 found adhering to the outer wall of the funnel, but its function was not 

 ascertained; it is shown in Plate IX., fig. 3 (It.). A thick-walled narrow 

 tube lead from the funnel to the spiral intestine. The stomach did not 

 appear to exist as such at this period. The connecting tube mentioned 

 above, and depicted in Plate IX., fig. 3 (c.t.), was slung from the oesophagus 

 by a tough mesentery. It entered the wall of the funnel where the latter began 

 to dilate, and ran in the wall of the funnel for a short space, finally opening 

 into the funnel. As before stated, this tube enters the spiral intestine ; if 

 this portion of the connecting tube is persistent it probably becomes the 

 pylorus of the adult, and accounts for the remarkable constriction at the 

 entrance to the spiral intestiue. The intestine lead into the rectum, which 

 opened into the cloaca. The rectal gland was a club-shaped diverticulum 

 opening into the rectum on its dorsal aspect. 



The large bi-lobed liver occupied the greater part of the abdominal cavity 

 anteriorly. The oviducts were formed, but, as was previously mentioned, 

 there were no traces of ovaries. The kidneys could be seen on the dorsal 

 wall of the body cavity. A pair of tubes lying anteriorly to the kidneys 

 were thought to be the abortive anterior portions of the Wolffian ducts. 



The brain and nervous system were much decomposed, but had apparently 

 reached their full development. The spinal column was composed almost 

 entirely of sectile cartilage, which, however, showed signs of incipient 

 thickening in certain areas, foreshadowing the osseous plates in the vertebrae 

 of the adult which have been described by Owen* and by Tate Regan. f 

 The notochord persisted as a transparent gelatinous substance in the inter- 

 spaces letween the vertebrae. 



The oral and pharyngeal linings were beset with hollow papillae throughout 

 the area which ImmsJ has described as covered with denticles in a specimen 

 measuring 790 mm. (about 31 inches). Microscopic examination failed to 

 reveal denticles, even in an incipient condition, in the skin of the mouth 

 and pharynx of the embryos under consideration. 



The most noteworthy feature of the internal structure was the condition 

 of the arterial arches. In the majority of the present-day sharks, with the 

 exception of the Notidanoidei, the ventral aorta breaks up into five arches. 

 The posterior pair of afferent branchials leaves the ventral aorta on its dorso- 

 lateral aspect, and supplies the fifth gill pouch. The next two arches, that 

 is to say the fourth and third afferent branchials, leave the ventral aorta on 

 its lateral aspect at varying intervals. Anteriorly the ventral aorta bifurcates, 

 and its right and left branches thus formed bifurcate again to give the second 

 and first aortic arches. This condition was realised in the young porbeagles, 

 but in specimen B in addition there was a sixth aortic arch, whose branches 

 left the ventral aorta on the dorsal aspect slightly posterior to the origin of 

 the fifth aortic arch (Plate IX., fig 4). The origins of these vessels were 



* The Anatomy of Vertebrates, Vol. I. , p. 33. 

 t Proc. Zool. Soc, 1906, p. 742. 

 ZProc. Zool. Soc, 1905, Vol. I., p. 44. 



