480 Causes and Course of Organic Evolution 



amongst nemerteans, and even in Rhabdocoela and in Rotifera. 

 Amongst apodous and urodele batrachians these tactile hairs 

 are most persistent, and as a rule most abundant, around 

 the anterior head region and the lips, where they are inner- 

 vated by fine branches of the trigeminal nerve. But they 

 are often abundant along the entire length of the animal, 

 mostly arranged in rows. They are supplied by the vagus 

 and by the hypoglossal nerves. Like the hairs of mammals, 

 these sensory hairs of cyclostomes and batrachians are purely 

 epidermal formations, and though greatly simpler in structure 

 result from invagination of the epidermis, which forms a fol- 

 licle round a central cell mass from which the clear hair springs. 

 Were more abundant cell-divisions to take place in the follicle, 

 and specially in the hair, a structure would result that would 

 closely approximate, in origin, in relation, in morphology, 

 and in function, to the stronger and more persistent hairs 

 of mammals. Like mammalian hair-cells also these are often 

 pigmented or contain fatty products. Such an origin has 

 already been suggested by Maurer (156: 717). A possible 

 connection may exist also between two conditions observed 

 by Schultze and Meijerle respectively. The former found 

 amongst Batrachia that each hair-area might develop as few 

 as one, as many as eight straight stiff hairs (157: 370). The 

 latter has shown that amongst mammals the hairs, instead 

 of being scattered, irregular, and so-to-say unsystematized, 

 may arise in groups of 3, 5, 6, 12, etc., which may either be 

 equal or unequal in size (158: 312). 



In this connection it is significant to observe that the first 

 mammalian hairs to appear during development, and the last 

 to disappear by specialization or degeneracy, are the sensitive 

 tactile hairs round the mouth, ears, eyes, along the lateral 

 line, and at times also along the fore limb, when this is used 

 in a specially sensitive manner. But these are the hairs which 

 are most primitive and persistent along the entire nemerto- 

 vertebrate line. 



In view of the al)ove evidence an origin for the haired mam- 

 mals from the urodele amphibians seems strongly suggested. 



