January, 190?,.] 



KNOWLEDGE, 



the pigeon. la the swollen throat we may get an inkling of 

 the origin of the remarkable wind-bag of our British bus- 

 tard. For it is easy to see that a similar throat-swelling in 

 the ancestors of this bird may have given place to a pocket- 

 like structure which in course of time increased to form 

 what, for the sake of the simile, we may call the stocking- 

 shaped bag of to-day. The gradual increase of the pocket 

 to its present proportions is to be attributed to the fact 



Fto. 2, — Dissection of the lu^ht m.Ii- ul the neck of tl\e Great 

 Bustard, Otix tirda, to show Ihe hour-glass. shaped gular pouch. 

 Drawn from the specimen in the British Museum. C, Crop ; 

 .fir, Hyoid ; Oe, Oesophagus ; I', Pouch; T, Trachea; /'Vascular 

 tissue, investing the upper part of the poucli. 



that the birds with the largest throat pouch found most 

 favour with the females of the community and were 

 selected on this accc^unt as mates. The birds with the 

 largest throat pouches being selected in each succeeding 

 generation, the jiresent race, with its enormous wind-bag, 

 was produced. 



The only other bird with a throat i>ourh tilled in the 

 sanio wav as that of the great bustard is the Australian 

 musk-duck (JJir.iura lohata). Tlie males only bear the 

 pouch, wliieh differs consi)ieuously from tliat of the 

 bustard in that it is external, hanging down, purse like, 

 from the lower jaw. Nothing, however, ajipears to be 

 known as to the use to whicli the jioueh is put, but there 

 can be little doulit but that it is a purely sexual character, 

 and displayed as a charm during courtship. 



Many lizards possess throat pouches of this kind, but 

 whether they are in all cases used exclusively for the 

 purposes of disjilay we do not know ; on this point 

 oltservation by travellers is silent. In many eases the 

 inHation of the pouch is accompanied by a display of 



brilliant colour over its surface. For example, in one of 

 the iguanas, Anolig carnlinensis, of the south-eastern 

 United States, the pouch, when pliicid, is white with a 

 few lines and spots of red, but at the moment of inflation 

 it tiecomes suffused with a l*rilliant vermilion. 



The curious but unsightly air-sac of the adjutant stork 

 may well close this series of examples of ornamental wind- 

 bags. Doubtless many of our readers have watched, in the 

 London Zoological Gardens, the ease and rapidity with 

 which this sac can be filled and emptied. Lik» that of 

 the great bustard it is a specially developed structure, and 

 quite distinct from the gullet. Unlike the pouch of the 

 bustard, however, its general form and proportions, both 

 when inflated and when empty, are visible externally, for 

 it is quite pendulous, and covered only by the bare skin of 

 the neck. Moreover it is present at all seasons. Empty. 

 it looks like a small conical Itag projecting from the front 

 of the neck, but when filled, its shape is completely 

 changed since it forms a bladder-like body a foot and a 

 half long. The method of inflation is quite unique, the 

 pouch communicating with a large cavity below the orbit 

 on the left side of the base of the skull, and this opens 

 directly into the nasal cavity. 



WHORLS AND CRESTS OF HAIR AS 

 ANIMAL PEDOMETERS. 



By Walter Kidd, .m.d., f.z.s. 



The works of man which he devises for his physical and 

 mental advancement are marked by a precision varying 

 with the degree of maturity of his science, and one of the 

 smaller among these is the pedometer, an instrument 

 requiring here no description. By a somewhat elastic use 

 of the idea of a pedometer, one may find among the 

 phenomena of nature certain which may be termed animal 

 pedometers ; these, like all the products of nature's handi- 

 work, are lacking in the exactness of human appliances. 

 But they are none the less significant of certain habits 

 belonging to the animals which possess them. 



Comparatively few animals can be said to carry about 

 on their bodies "a register of their locomotive activity as a 

 cyclist does on his machine, or a pedestrian in his pocket. 

 Nevertheless, those few mammals that display jiedometers 

 on their hairy coats, " iirbe et orbi," show an advance in one 

 particular upon any of man's pedometers, inasmuch as 

 fairlv clear records of ancestral as well as individual 

 activities are indicated. The phenomena here looked upon 

 as animal pedometers arc those arrangements of hair 

 which we know as whorls, found in various regions of the 

 bodies of animals, and seldom in any but the short-coated 

 forms. These whorls do not often exist alone, but usually 

 are associated with a feathered arrangement which pr^K•eeds 

 against the general stream of hair adjoining them, and 

 this feathering generally terminates somewhat sharply in 

 a ridge or crest. Whorls, featherings, and crests then 

 constrtute a fullv-formed •' pedometer" in this connection. 

 The best examples of these, and the most familiar, are 

 those seen on the horse, and they are so far removed from 

 being accidental or indifferent phenomena, and are s.i 

 clearly brought under certain simple laws of physical 

 causation, as not only to deserve but to demand interpre- 

 tation. Few thoughtful persons will dissent froiu the 

 remark in the coiiciusi(m of Jevon's Principles of Science, 

 where he savs. "Now among the most unquestionable 

 rules of scientific methods is that first law that irhaterer 

 2>heiiome)ioii la. I». We must ignore no existence whatever ; 

 we may variously interpret or explain its meaning and 

 ori>,nn,"bul if a ]>henomeuon does exist, it demands some 



