426 



TEE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



upon the primitive condition of the eyeless ani- 

 mals of the Mammoth Cave. The eminent zoolo- 

 gist declared the necessity of a series of observa- 

 tions and experiments to arrive at absolute cer- 

 tainty. He advised the attempt to rear the em- 

 bryos of the cave-species by subjecting them to 

 different conditions from those in which they are 

 now found ; and he ended with this declaration : 

 " According to all that I know of the geographi- 

 cal distribution of animals, I am satisfied that 

 these were created iu the circumstances in which 

 they are now living, within the limits where they 

 are now found, and with the same peculiarities 

 of structure that mark them to-day." Only those 

 who refuse to deal with the observation of facts 

 can be easily led to believe that the inhabitants 

 of caverns — fish, insects, or other animals — are 

 blind because they live and breed constantly 

 amid circumstances iu which the organ of Bight 

 could not do its duty. That supposition is really 

 not inadmissible, according to the laws of organic 

 development ; an atrophy may be produced under 

 certain influences ; but a knowledge of the con- 

 ditions of life rigidly fixed for animals in general 

 compels us to reject such an explanation as that 

 with regard to the cave-species. There is almost 

 an absolute certainty that species designed to see 

 the day would perish, or cease to breed, if they 

 w r ere confined in an atmosphere laden with moist- 

 ure, and plunged in utter darkness. Since the 

 date of Agassiz's expressed opinion, these sight- 

 less species have been collected in great num- 

 bers, and observations repeated, and on one point 

 of the highest importance doubt is no longer 

 possible ; the animals of these dark recesses are 

 not found in spots exposed to light, and many of 

 them differ so strikingly in their characteristics 

 from species which see as to destroy any notion 

 of community with them in origin. 



After the instances of adaptation of external 

 parts to fixed conditions of existence, we should 

 examine in what way the parts of internal organ- 

 ization explain special aptitudes. In this regard, 

 the absolutely precise facts we possess are not 

 yet so numerous as might be wished, but there is 

 reason to expect a great deal from the investiga- 

 tions that are going on in our time. 



In 1853, the first living hippopotamus seen in 

 Europe since the time of the Romans was intro- 

 duced into the menagerie of the Museum of Nat- 

 ural History at Paris. It was an event, and every 

 one was delighted in watching the singular ways 

 of the animal, of which the pictures and descrip- 

 tions and stuffed figures had given no correct 

 idea. The new guest at the Jardin des Plantes 



often plunged into his bath, and reappeared at 

 the surface almost immediately ; but several 

 times the animal made so long a stay at the bot- 

 tom of his basin, that more than once it caused 

 uneasiness. As it was -not understood how a 

 mammal of that order could have the power of 

 breathing at very long intervals, suffocation 

 seemed possible. But all anxiety ceased when 

 the conviction was gained that the hippopotamus 

 staid at the bottom of the water because it was 

 his pleasure to do so, and after that there was no 

 longer any doubt that it possessed some organic 

 arrangements fitted for an amphibious animal. 

 An opportunity of studying them came later. 

 The first hippopotamus was a male ; a female 

 arrived, and they produced offspring. Several 

 of the young died, and Gratiolet, whose eloquent 

 lectures have charmed so many audiences, de- 

 voted an attentive examination to them. That 

 examination supplied the explanation why it is 

 that suffocation would occur in the hippopotamus 

 only after a very long suspension of respiration. 

 Several remarkable arrangements of the veins 

 force the blood to accumulate and pause, not to 

 rush suddenly to the heart, nor to return in a 

 great quantity to the lungs. Thus the animal, 

 protected against the danger of congestion of 

 the brain, the eyes, the lungs, and even the mus- 

 cles, preserves its freedom of movement. 



Bats, and those pretty little paroquets called 

 inseparables, from the notion of the mutual af- 

 fection these charming birds require, the agapor- 

 nis of zoologists, suspend themselves by their 

 claws, and sleep head down. In that position 

 most animals would suffer congestion of the 

 brain. Such an accident need not be feared 

 either for bats or for paroquets. We under- 

 stand how so unusual a position is possible for 

 these animals, as soon as we remark the number 

 and arrangement of the little valves in the veins 

 of the head and the fore-parts of the body. The 

 immense difference that exists between birds as 

 to their power and rapidity of flight is well known. 

 The pheasant and partridge have a short and 

 heavy flight; the sparrow is not one of the most 

 favored birds in this respect ; the eagle, the fal- 

 con, the sea-mew, on the other hand, are wonder- 

 fully endowed in regard to flight. Who has not 

 admired, on fine evenings, the dizzy, darting whirls 

 of the great swallow ? No doubt the relative di- 

 mensions of the wings, the general shape of the 

 body, permit us to account in a certain degree for 

 the greater or less ease of movement in birds ; but 

 this unequal distribution of the power of locomo- 

 tion is not due merely to the proportions of the 



