66 THE GENERAL ANATOMY OF THE LEMUROIDEA [SECT. A 



found in certain rodents and insectivores, is said to be wholly 

 unrepresented among the Lemurs.] The fifth group of vibrissae 

 is on the forearm and near to it a cutaneous callosity may be seen 

 in some varieties 1 . 



The eye-lashes arise not from the margin of the eyelid but 

 from its external aspect. 



As regards the general hair-covering 2 , the direction of the 



1 Bland Sutton and Beddard. Cf. Nature, Jan. 9, 1902, p. 222. 



2 The arrangement of the hair-tracts in the mammals generally, and particularly 

 in the Primates, possesses an extensive literature. To the valuable memoir by 

 Schwalbe on the Lemurs (cf. footnote p. 65) must be added a subsequent and 

 more exhaustive monograph on the Anthropoidea by the same author, by whom a 

 full bibliography is provided (Schwalbe, 1912, " Tiber die Richtung der Haare bei den 

 Affen-Embryonen," Selenka's Studien fiber Entwicklung, u.s.w., zehnte Lieferung). 

 A notable feature of this work is the presentation of the author's views as to the general 

 significance of the marked variations in the details of hair-tracts in reference to 

 their direction and distribution. This subject has been studied also by Dr Kidd, 

 who in 1903 published an account of his work (The direction of Hair in Animals 

 and Man, 1903). Both authors agree in assuming the existence of a primitive type 

 of distribution, such as that described above (p. 65) in which the hair is directed 

 uniformly backwards (cranio-caudally) from the nose to the tail. This primitive 

 and simple distribution has undergone many modifications in different animals. 

 Dr Kidd invokes the influence of a number of mechanical causes, such as the action 

 of gravity (cf. the Sloth), the habitual assumption of certain attitudes, or repetition 

 of movements, and finally the relation to points called "fixed" as regards the 

 action of subjacent muscles. To complete this account, it is necessary further to 

 postulate a purely Lamarckian transmission of acquired characters. Professor 

 Schwalbe, in rejecting these views, lays stress on three capital factors as accountable 

 for the majority of the observed phenomena. Thus reference is made to (i) the 

 occurrence of flexions (Faltungen) as at the throat, elbow or knee, when the hairs 

 on either side of the angle will grow in the lines of least resistance and produce 

 consequently divergence from or convergence towards a point. Again (ii) a localised 

 depression of the skin, in conformity with the growth of the local tissues, will be 

 followed by an analogous re-arrangement of the primitive tracts. Finally, (iii) the 

 mode of increase in the surface area of the skin, and of the epidermis in particular, 

 is evidently not uniform all over the body. Professor Schwalbe shews by an in- 

 genious model that if such irregularity be granted, the production of hair- tracts in 

 definite directions is a necessary consequence. (This part of Professor Schwalbe's 

 position is not unlike the view expressed originally by Voigt.) 



Professor Schwalbe thus throws back the basis of an interpretation of hair 

 vortices, spirals, etc. upon the phenomena of growth, whereby folding and other 

 irregularities of surface are produced. Many factors enter into these phenomena, 

 such as the mode of life and consequent modifications in the details of form. At 

 this point there seems to be an approach to the position adopted by Dr Kidd. Yet 

 the latter, as we have seen, postulates causes acting directly from without, whereas 



