16 S. B. VINCENT 



midway striking the walls of the superior enlargement above. 

 It has been said by Botezat, Szymonowicz and others that the 

 ringwulst only surrounds the follicle from two-thirds to three- 

 fourths of the circumference, but in the white rat this is not so. 

 The tissue is very fragile and in most of the methods of prep- 

 aration it is badly torn, but with silver nitrate and osmic acid 

 the structure is often whole and entirely surrounds the follicle. 

 It shrinks much in staining, in length as well as in width, which 

 may account for the gap one often sees in the circumference. 



This very tender organ consists of almost transparent connec- 

 tive tissue fibers which enclose large pale nucleated cells. In the 

 rat, in a longitudinal section, the structure has somewhat the 

 shape of a lung which comes out by a stalk from the follicle walls 

 and hangs suspended in the cavity of the sinus. It is traversed 

 in all parts by loops of capillaries which are unusually large for 

 the size of the organ (fig. 7). 



As one looks down upon it in well prepared sections it seems 

 covered with fine varicose fibers which run from the base out to 

 the periphery and end with a few fine branches or with small 

 varicosities (fig. 6). Whether these are sensory or vaso-motor, 

 I have no way of knowing. 



The ringwulst is not found in all animals according to Bonnet 

 and others. The horse, cattle and swine are without it while in 

 carnivora and rodents it is fully developed. Botezat ('97, p. 144) 

 shows, however, that some animals, as the swine, have two 

 kinds of tactile hairs; those with and those without a ringwulst 

 and a ring sinus. Where there is no ringwulst as in the horse, 

 there are often, Bonnet ('78, p. 348) says, similar thickenings on 

 the walls of the trabeculae near the conical body or else where 

 several such walls come together. These thickenings may serve 

 the same purpose as the ringwulst, whatever that may be. 



V. COMPARATIVE ANATOMY 



Hair is a mammalian characteristic, but the tactile hair is 

 probably phylogenetically the first to appear and when all other 

 hair is lost, as in the whale, a few of these still persist about the 



