M A M M ALIA. 



I'M 



into the account that the arms tell much more in 

 swimming than they do in walking. In walking, 

 from the comparatively trifling resistance in the air, 

 the arms can be regarded as very little else than 

 balancers ; whereas in swimming they are real organs 

 of progressive motion ; and as in advancing them to 

 the front they can be feathered, as a rower feathers 

 his oar, so as to offer much less surface to the water 

 than they do when striking against it to give the 

 forward impulse, skilful management may convert 

 them into very efficient swimming instruments. There 

 are several circumstances connected with the pressure 

 of water, when the body pressed on is completely 

 immersed and under the surface, which are not un- 

 worthy of attention. Among these we may mention 

 how much more easily the body of an animal is lace- 

 rated, or any substance cut by a sharp instrument. 

 The substance stands up to the instrument, both on ac- 

 count of the compactness of its parts, from the pressure 

 (if it be a compressible body), and also from the water's 

 keeping it against the cutting substance, being so much 

 greater than that of atmospheric air. Owing to these 

 effects of water, many substances can be cut when 

 submerged by means which have no influence upon 

 them, when the attempt is made in the common air. 

 As an instance of this, it is said that, under water, 

 glass may be cut into any shape by means of a pair 

 of common scissors ; whereas, in the atmosphere, it 

 cannot be cut by the same instruments without a 

 very great effort, and that effort splinters it to pieces 

 instead of cutting it in any definite direction. 



So far as we are aware, atmospheric air and water 

 are the only fluids in which any of the mammalia can 

 live, if they are fairly submerged, or included in the 

 volume of them. The common mammalia which re- 

 quire very frequent respiration of the free air cannot 

 remain for any length of time under water; and 

 therefore, in their progressive motions through that 

 liquid, which are not swimming in the proper sense 

 of the term, but merely a species of walking, except 

 in the case of man, who brings into play in this situa- 

 tion his arms and hands which are not available for 

 locomotion in ordinary cases, they require to keep 

 the nostrils, or entrances to the breathing apparatus, 

 above the surface, otherwise they soon get suffocated 

 by the entrance of water into the lungs. The vulgar 

 notion is that the water thus taken into the cavity of 

 the land mammalia when they are submerged is taken 

 into the stomach, but this is a mistake, for nothing 

 can be taken into the stomach but by an effort of 

 swallowing ; and even though water were taken into 

 that viscus, in as great quantity as the pressure of a 

 moderate depth could force it, it would do no great 

 harm, if it did any harm at all. But when the water 

 gets into the cells of the lungs, the case is very dif- 

 ferent. It not only prevents the contact of atmospheric 

 air with the capillary vessels for the time that the 

 animal is in the water, but it lodges in the cells ; and 

 as the lungs are capable of expelling only air, toge- 

 ther with the quantity of water which it may hold in 

 a state of vapour, and this differs in different mam- 

 malia according to their temperature, there are no 

 natural means of expellin? the water or restoring the 

 animal, without it can be so inverted as to make the 

 water run out, and that the lungs can be so excited 

 by some stimulus as to promote the expulsion. 



The old opinion was, that in the human subject, 

 and by inference in all the other land mammalia, if the 

 foramen ovale or internal passage between the syste- 



matic side of the heart and the pulmonary, which exists 

 in the foetal state, could be kept open, life would be 

 preserved for a long time under water. This, how- 

 ever, is not the case, for it is the want of atmospheric 

 stimulus to the blood and not the want of passage 

 which causes strangulation, in drowning, and in every 

 other case in which atmospheric air is not freelv 

 admitted into the lungs ; and this particular passag'e 

 in the heart is of use only as long as the young ani- 

 mal receives its nourishment from the arterial blood 

 of the mother, which blood has already undergone 

 the requisite operation of the air in respiration, and 

 though it were kept open in after-life it could be of 

 no service whatever. 



Mammalia, whose habit it is to remain for a con- 

 siderable time under water, do not so remain in 

 consequence of any passage in the heart resembling 

 the foramen ovale. They so remain, because the 

 volume of their lungs is proportionally larger than 

 that in animals which must breathe more frequently 

 and therefore cannot remain so long under water ; 

 and besides this, such animals are generally provided 

 with some sort of valves closing by pressure from 

 without, by means of which water is excluded from 

 the lungs, and the more completely excluded in pro- 

 portion as its pressure is the greater. We find a 

 provision of this kind in the otter and the seal, and in 

 the cetacea it increases in proportion to the length of 

 time which the animals can remain under water. In 

 the fresh water cetacea it is less perfect than in the 

 marine ones which inhabit near the shores ; and in 

 them again it is less perfect than in those which 

 range wide oceans, and are capable of descending to 

 great depths, as is the case with the whale. The 

 blow-holes are the proper breathing apertures of such 

 animals, and their mechanism is perfect in proportion 

 as the animals are capable of plunging. It must be 

 borne in mind, that though these animals throw up 

 jets of water when they blow, they do not do this 

 always when they breathe ; and that when they do 

 it, the water has never by any chance come from the 

 lungs, any more than substances which are sometimes 

 returned by the nostrils of land animals come from 

 their lungs. The water thus discharged is the cur- 

 rent which sets toward the gullet of the animal in its 

 feeding, and as both the gullet and the entrance of 

 the trachea are shut against it, it is carried upward to 

 certain cavities in the bones of the head, to which 

 the under passage is by valves opening inward of the 

 cavity, and the upper passage by valves opening out- 

 ward. When these cavities are full of water the 

 expired breath from the lungs blows it out with con- 

 siderable force, which is the cause of the jets which 

 are sent up from the blow-holes. There are, how- 

 ever, many circumstances in the adaptation of aquatic 

 mammalia to the element in which they spend the 

 greater part of their time, that it would be impossible 

 to notice in a sketch so limited as this ; and so we 

 must proceed to our notice of the organs of motion 

 as fitted for the land, and the several adaptations 

 which are connected with them. 



As is the case with mammalia which originate the 

 individual portions of their motion from a fluid ful- 

 crum, so with those which originate these from a solid 

 fulcrum, there are two sub-classes or orders ; namely, 

 climbers or those which ascend or descend upon 

 trees, or other substances standing up from the sur- 

 face of the earth, and walkers, or those which have 

 the line of their motion parallel to the earth's surface. 



