248 CETACEA. 



which is great in respect to land animals, would, in water, be 

 comparatively weak ; this defect is, in the case of the Cetacea, 

 supplied by the spherical form and great refractive power of the 

 lens of the eye. The outer, or sclerotic coat is, in these animals, 

 remarkably thick and tough, it being as dense as tanned leather, 

 serving both to preserve its spherical form, and to defend the ani- 

 mal from injury. This coat increases in thickness towards the 

 back part, and is full five times the thickness behind, that it is 

 on the front part. To this, Dr. Paley (see Nat. Theol.) has 

 well referred, as strikingly evincing Divine contrivance. The 

 front part sustains the pressure from without, and needs no addi- 

 tional support; but were the back part to yield, the globe of the 

 eye would be distended in that direction, and the whole interior 

 of the eye suffer derangement. As a safe-guard, the sclerotic 

 coat is, therefore, remarkably strengthened behind. 



One of the most extraordinary things in the economy of the 

 Cetacea, is the length of time during which they can suspend 

 respiration. While, in most animals, it can be suspended only 

 for a few minutes, in some of the larger whales it may be sus- 

 pended from one to nearly two hours, they remaining under 

 water for that time. This fact points to the peculiarity of their 

 breathing apparatus. The whale has a reservoir wherein there 

 is an overplus of oxygenized blood which, on occasion, is emptied 

 into the general circulation ; it is thus able to continue longer 

 under water, and less frequently resorts to the surface in order 

 to inhale oxygen from the atmosphere. Whales have no nostrils, 

 properly so called, and their mouths are seldom opened in the 

 free air. The process of breathing is therefore carried on 

 through tubes, called blow-holes, or spiracles, opening on the top 

 of the head, and allowing a free passage to and from the lungs. 

 These openings are called blow-holes, because the expulsion of 

 the long-confined and heated air, as the animal rises to the sur- 

 face, is attended with considerable noise, and the casting forth of 

 water or steam. The " spoutings " are heard as far as two miles, 

 and sometimes reach the height of twenty or thirty feet. They 

 are most conspicuous in the larger genera ; quite marked in the 

 intermediate dimensions; but in the smaller, seldom or never vis- 

 ible. After the "spoutings are out," as the whalers say. most 

 of the Cetacea descend into the depths of the ocean. The lungs 

 are guarded from injury that might hence arise, by the conical 

 stopper which, like the cork of a bottle, fits itself to the blow- 

 hole so perfectly, as to exclude every drop of water. Habitually, 

 the whales take their sustenance under water; but, "by a slight 

 alteration in a few cartilages at the top of the windpipe, and in 



