THE INTEGUMENT AND THE EXOSKELETON 101 



he hair of the two sexes is of equal length, but in those with 

 vavy or curly hair that of the female considerably exceeds in 

 ength that of the male. 



The hair exhibits a definite slant or direction of growth, 

 which varies in different parts of the body, so that one may 

 speak of hair-streams or hair-currents. This direction is the 

 one shown by the follicle and by the hair immediately after 

 its emergence from the skin, and is entirely unrelated to the 

 various directions which the free masses may temporarily 

 assume under the influences of gravitation, wind, or other 

 external forces. It is thus best seen in animals with a coat of 

 short, appressed hair, like horses or short-haired dogs, and is 

 often quite obscured in those with long hair, or in those with 

 soft, plush-like fur, like seals and moles. In these latter, 

 however, it may be accurately ascertained by shaving or clip- 

 ping the hair. 



In general it may be said that a given area shows a defi- 

 nite direction, the lines of which may be parallel or some- 

 what divergent, two adjacent areas being separated either 

 by a parting, where the streams diverge from one another, or 

 by a raised crest or seam where they converge. At certain 

 points special features may be noticed, the most important 

 of which are the vortex or whorl, the rhomboid and the feath- 

 ering. In the vortex variously directed hair currents unite 

 to form a spiral figure, which either converges to form a 

 central tuft, convergent vortex, or starts at the center and 

 diverges, divergent vortex. The first type of vortex often 

 marks a point at which some projecting ojgan is later to ap- 

 pear, as at the corners of the forehead in the calf before 

 the appearance of the horns ; or else one where a former pro- 

 jecting organ has disappeared, as at the umbilicus ; but, on the 

 other hand, there are numerous instances where such a rela- 

 tionship cannot be established. The significance of the second 

 type is unknown. Either type may form either a right- or a 

 left-handed spiral (clockwise or contra-clockwise). A rhom- 

 boid is an open space of the shape designated by the name, 

 and appears where the corners of four areas meet. It is thus 



