

TIE INTEGUMENT AND THE EXOSKELETON 99 



placed by the permanent coat, which usually shows but slight 

 development save in certain definite localities. The lanugo 

 persists in a reduced condition on the face, especially in females, 

 iorming the down which gives to the cheeks their character- 

 stic bloom. Abnormal hairiness in man, or hypertrichosis, 

 s fortunately rare, and is of two kinds ; the one, hypertricho- 

 ris vera, is due to an excessive growth of the permanent coat 

 which, replaces the lanugo ; the other, pseudohypertrichosis, is 

 :he result of the persistence of the lanugo. 



Localized hypertrophy in various mammals in the form of 

 nanes, crests or tufts of hair, is of frequent occurrence and 

 LS used for various purposes, such as defense from flies or 

 Dther noxious insects, attraction of the other sex, or as a pro- 

 ection from the teeth of rivals. Under this general head 

 :ome also the beard of man, which corresponds in position 

 ind direction to that found in other primates, and the long 

 lair of the head. The other locations in Man in which long 

 lair occurs, the axillary and pubic regions, do not seem to 

 )elong here, and probably represent portions that escaped 

 reduction rather than hypertrophy. The obvious function of 

 the cranial hair is a protection from the sun, and its location 

 uggests that it is developed with reference to the erect and 

 not the quadrupedal position, in which latter case it would 

 ; aave extended farther down the back. The axillary and pubic 

 ufts may be for lessening the friction between the limbs dur- 

 ng motion ; it has been also suggested that they possessed a use 

 n transitional forms in furnishing places to which the infant 

 might cling, thus leaving the arms of the parent free for 

 :limbing. In support of this latter view it may be noticed that 

 he distances between these locations correspond approxi- 

 mately to the proportions of a normal infant, and that an in- 

 r ant thus attached is also in the right position for nursing. 



Aside from differences in caliber and length, the hair of vari- 

 ous mammals differs markedly in structure, in color, in the 

 hape of its cross-sections in various places and in the shape 

 issumed by each hair. In structure a hair consists of a firmer 

 :ortex of varying thickness enclosing a softer medulla; a 



