86 The Unity of the Organism 



ferent orders. Nevertheless their similarity in food and 

 other habits makes this difference in odor interesting. 



The great variety not only as to form and secretion but 

 as to position on the body, of the scent glands in the mam- 

 malia has an obvious bearing on the topic in hand. The 

 abdominal glands of the shrew-mice, the hip glands of the 

 mouse genus Microtus; the leg glands and foot glands and 

 suborbital glands of the deer family ; the anal glands of 

 many orders; and the almost universal presence of glands 

 whose secretions are odoriferous connected with the sexual 

 organs, may be mentioned as illustrating the wide distribu- 

 tion of such structures in the body. And it is noteworthy 

 that these may be present or absent in closely allied forms. 

 Thus the Indian rhinoceros (Rhinoceros indicus) is said 

 to have hoof glands while the Sumatran species (Rh. Su- 

 matrensis) has none. 11 



The well known fact may also be recalled that scent 

 glands are often distinctive of the sexes. The musk-deer 

 (Moftch'H'S moschiferus) affords a particularly striking il- 

 lustration of this, not merely as to the production of the 

 perfume which makes this animal famous, but as to a glandu- 

 lar secretion of quite another sort. In the adult male there 

 is a naked area around the root of the tail which is, as 

 Darwin expresses it, "bedewed with an odoriferous fluid." 

 This area is neither devoid of hair nor secretory in the 

 female at any time in life, nor does it appear in the male 

 until he is two years old. That the musk-gland of this 

 species is a strictly masculine affair goes without saying 

 when it is recalled that it is connected with the male sexual 

 organs. 



Ants are particularly instructive from this as from many 

 other standpoints, the sense of smell in them being of far 

 greater importance relatively to the other senses than in 

 the higher orders. This has been established particularly 

 by the admirable researches of Forel and Wasmann. Cor- 



