March, 1903.] 



KNOWLEDGE. 



53 



by disguise, making itself as thin and shadowy as possible 

 by compressing its sides, and then, turning itself so that 

 only the thin edge is presented to the enemy. This done, 

 it next endeavours, by a dexterous turn, to place the twig 

 upon which it is resting between itself and the attacking 

 party. By this ruse it often snec'eeds in effecting the 

 vanishing trick and disappointing its would-be captor. 

 If, however, this plan fails, then the body is as suddenly 

 transformed by inflation. Thus the passive disguise is 

 thrown off and a threatening attitude assumed which is 

 probably generally successful. This inflation is effected 

 partly by inflating the lungs, which have a quite unique 

 structure, inasmuch as they are produced backwards into 

 several blind finger-like sacs which extend far down the 

 body-cavity, and partly by means of a large air-sac in the 

 throat. The purpose of this sac, however, is by no means 

 concerned exclusively with the work of inflating the throat. 

 It probably serves also as a reservoir for air when the 

 entrance to the windpipe is closed by the peculiar 

 mechanism of the tongue in catching insects ; and is used 

 also in the production of a peculiar hissing sound which 

 the creature makes when angry. 



An agamoid lizard, Agama sanquinolenta, common in 

 the deserts of Turkestan, also resorts to the use of a 

 throat-pouch to make itself appear more formidable. The 

 males of this species are very pugnacious, especially during 

 the breeding season. At this time, when about to attack, 

 the throat-sac is inflated till it attains the size of a walnut, 

 the body is raised upon the legs, the head lowered and 

 turned inside, and the foe stealthily watched. Suddenly, 

 with a dart, the attack is delivered, and, if the fates are 

 propitious, the enemy is routed. 



Among birds and mammals, as among the frogs and 

 their kind and the reptiles, the practice of magnifying the 

 size of the body, apparently with a desire to terrify their 

 enemies, is also followed. The birds effect this by erecting 

 the feathers, the mammals by causing the hair to stand on 

 end. Certain of tiie latter, however, have developed special 

 storm signals. The bladder-nosed and elephant seals have 

 been conspicuously successful in this. The latter is so- 

 called from the snout which is produced into a short 

 trunk, flaccid while the animal is quiet, but capable of being 

 inflated and erected when enraged. The wind is forced in 

 through the roof of the mouth. The old sealers, it is 

 said, used to regard the trunk of the elephant seals they 

 killed as a great delicacy, calling them " snotters." The 

 inflatable headgear of the bladder-nosed seal is no less 

 remarkable than that of its brother of the elephantine 

 nose. Indeed, the two structures are really not very dis- 

 similar ; for did the inflatable tissue of the first-named 

 extend forward somewhat further a proboscis precisely 

 similar to that of the elephant seal would result. As large 

 as the rest of the head when fully inflated, this peculiar 

 casque is a purely secondary sexual character, being found 

 only in the males. It seems to be used as a signal of 

 defiance, being raised whenever its owner proj)oses to give 

 battle to such neighbours as may desire to while away the 

 tedium of doing nothing by a friendly bout with the teeth. 

 At such times a quivering motion is given to this curious 

 casque, and this undoubtedly adds not a little to the 

 effectiveness of its appearance. 



The Gavial, one of the Crocodilia, is the only one of all 

 the reptiles which has developed a similar bladder-like 

 structure. In the full-grown male of this species {Gavialis 

 gamjdicns) the nostrils are seated in the middle of a pro- 

 minent hump. At the will of tlie animal this can be 

 inflated like a bag. The recoil of the air down the long 

 nasal passages, consequent on the inflation of this bag, 

 has produced a curious modification of certain bones of the 

 skull, resulting in the formation of a pair of hollow 



globular swellings of the size of a goose's eg^. So little is 

 known about the habits of this creature, in spite of the 

 fact that it is common enough in many of the rivers of 

 India, that the occasions when this bag is used, as well as 

 its exact purpose, has yet to be discovered. Possibly, 

 however, it serves the same purpose as that in the seals 

 just described. 



These curious nasal wind-bags are, in all cases, in con- 

 nection with the nostrils through which they are filled and 

 emptied. This fact recalls the existence of certain 



Fio. 1. — The Spotted Globe-Fish, Dlodon maciilatus. The upper 

 figure shows the animal when intlated, floating back downwards, that 

 in the right corner the normal condition. 



mysterious air-pouches in connection with the nasal 

 passages, which occur in the horse and the ass, and their 

 relations to the rhinoceros and the tapir. Familiar enough, 

 in the horse at least, to the comparative anatomist and the 

 veterinary surgeon, to whom these structures are known as 

 the " false nostrils," to the general reader their existence 

 is probably quite unknown. Let those who have the 

 opportunity examine carefully the margin of the upper 

 part of the nostril of the horse, when they will find the 

 aperture to what is really a blind pouch, from three to 

 four inches deep, conical in form, and lined with the same 

 smooth skin as that which lines the nasal passage. In 

 the tapir a similar but much more develoj>ed pouch is 

 found. In this animal it ruus upwards as a narrow tube, 

 at first in conjunction with its fellow of the opposite side, 

 and later separating, each taking a curiouslv curved or 

 convoluted course, and ultimately terminating in a blind 

 dilatation lodged in a distant groove in the skull bones 

 roofing the snout. In the rhinoceros a similar structure 

 is found, but intermediate in shape between that of the 

 horse and tapir. The "false nostril " of the ass, it should 

 be remarked, is larger than that of the horse. 



What the purpose of the pouches in these animals 

 may be is at present a mystery, but they probably are 

 remnants of a once useful structure. 



The nuTubor of creatui-es which have adopted the device 

 of imprisoning air, and the variety of uses to which it has 

 been put is indeed striking. So far our survey of this 

 subject has been confined to the higher animals oulv. Let 

 Tis now liriefly review some of the more striking cases 

 which are to be found among the more lowly :vnimals. 



Perhajis the most striking examples to be discovered 

 among these more humble creatures are those furnished by 

 certain jelly-fish which live in colonies and drift about the 

 surface of the open sea, suspended by living life-buoys. In 

 the form known as Phjigoiilwin, for example, an" enor- 

 mously elongated individual undertakes the work of 



