3 6o DISCOVERY REPORTS 



value in the present discussion 1 . It may be imagined that some chemical mechanism 

 exists for a more speedy transfer of oxygen from the blood to the fatty masses of the 

 retia, which may thus act as an oxygen storage mechanism. The retia may in fact be 

 capable of forming a sort of accessory lung. Since the vascular networks are under the 

 control of the somatic nervous system, they may possibly be engorged with blood at 

 will from the posterior thoracic artery, and this blood may perhaps be discharged at will 

 again into the posterior thoracic vein. The proximity of the retia to the heart is 

 extremely suggestive in this connection, since it implies that the blood has only a short 

 distance to travel before reaching the fatty masses where it is to be stored. Thus during 

 the successive inspirations which the whale takes at the surface before sounding, the 

 blood discharges oxygen into the fat of the rete, and this oxygen is subsequently 

 liberated into the circulation during the period of submergence. 



It has already been remarked that a greatly increased oxygen debt can be incurred 

 in the tissues if the brain and nervous system are kept supplied with oxygen. It is 

 possible that the rete may form, by means of its oxygen-charged fatty masses on the 

 anterior part of the spinal chord and around the hinder part of the brain, a means of 

 keeping the main nervous centres supplied with oxygen during submergence. The 

 basicranial rete may be looked upon as a secondary oxygen reservoir for blood destined 

 for the side of the head, face and orbit. 



According to this theory of the functions of the retia mirabilia it may be imagined 

 that during submergence blood returns to the heart, not through the postcava, but 

 through the intraspinous veins and the two great sinuses in the neural canal. Thus 

 venous blood from all parts of the abdomen and hinder extremities is made to pass 

 through the thoracic rete into the posterior thoracic vein. It thus enters the right 

 auricle after having been re-oxygenated in the rete. It might be expected that if this 

 actually takes place, and the heart, as a result of this process, receives already oxygenated 

 blood in the right auricle, some mechanism would exist for "short circuiting" the 

 pulmonary artery. No mechanism was found in the Fin Whale except that the ductus 

 arteriosus is very wide and has a spacious lumen. It might easily be imagined to lead 

 blood from the right ventricle into the systemic arch. Lacoste and Baudrimont (1926, 

 pp. 1148-50) found annular folds in the muscular walls of the pulmonary artery of 

 Delphinus delphis, which, the authors suggested, might have the effect of impeding the 

 flow of blood in that artery when fully erected in its lumen. Similarly the small intra- 

 pulmonary branches of the artery "se pulverisent en bouquets extremement touffus 

 d'arterioles tres onduleuses" the effect of which would also be to block the flow of 

 blood through the lungs. 



1 Sir Sidney Harmer has drawn my attention to the view held by many whalers and accepted by some 

 writers that the Sperm Whale descends to especially great depths. If this opinion is based on the duration 

 of the "sounds" which the Sperm Whale makes, we should expect to find in the oil of this species a 

 high oxygen solubility. The results tabulated on page 359 show, however, that the solubility is decidedly 

 lower than in other whales. The retia of the Sperm Whale were not examined in detail, but a superficial 

 inspection indicates that they are of even greater extent than in the Fin Whale. They can be seen within 

 the thorax as far back as, I think, the 8th rib. This might be expected if the oxygen solubility of the oil of 

 this species is less than that of Fin Whale oil. 



