50 COMPARATIVE ANATOMY 



tacea is augmented many hundred and even thou- 

 sand-fold ; for it is a fact, that the larger genera will 

 remain an hour, and sometimes nearer two, under 

 water. There must then be some essential pecu- 

 liarity in their organization, to account for this ex- 

 traordinary phenomenon ; and yet we know not that 

 any regular attempt at explanation has hitherto been 

 made. It is with considerable hesitation, therefore, 

 that we offer the following brief hints upon the 

 point. 



Respiration is in a great degree subservient to the 

 circulation of the blood : the stimulus to inspiration 

 is the accumulation of this fluid in the lungs, which 

 when purified proceeds to the heart, whence it is 

 propelled through the frame for the purposes of se- 

 cretion, &c. ; after which it is again received into 

 the veins, where it assumes its venous aspect, and 

 is deprived of its arterial character. The circle thus 

 described in man and the mammalia generally, is, 

 so to speak, continuous and simple. In the Cetacea, 

 however, it is not so; for in them the arterial 

 portion, instead of being a simple and direct course 

 to the venous, is complicated by the addition of a 

 structure which we believe is peculiar to this order, 

 and which is nothing less than a grand reservoir 

 for the reception of a great quantity of arterial 

 blood, which, as occasion requires, is emptied into 

 the general circulation, and thus, for a time at 

 least, supercedes the necessity of respiration. 



This structure was first noticed by John Hunter, 

 and with his usual minute accuracy; Dr. Barclay 



