STRUCT [JBE OF THE HATRS OF MYLODON LISTAI. 403 



seen to consist of I'ows of six or seven spherical spaces 

 arranged in the direction of the length of the hair. The 

 middle spaces of each series are the largest, and the terminal 

 ones the smallest, so that the general effect is that of a seg- 

 mented spindle. In the pigmented parts of the hairs the 

 pigment granules are disposed mainly around the smallest 

 air spaces at the ends of the spindles. The central part of 

 the hair is occupied by a slit-like air space partially filled 

 with a highly refractive substance, which shows no traces of 

 its cellular origin as the medulla so frequently does. The 

 basal part of the hair is more cylindrical in shape than the 

 middle part ; and the medullary cavity dwindles gradually 

 away, to disappear altogether in the part of the hair within 

 the follicle, or just outside it. The basal parts are trans- 

 parent, owing to the reduction in the number and size of the 

 air vacuoles. A section of the hair taken about 3 mm. out- 

 side the follicle is shown in fig. 15. 



Tamandua tetradactyla. 



In this ant-eater the hairs are less coarse than in Myr- 

 mecophaga, and have the form of slightly compressed 

 cylinders. The transverse section is oval in form, measures 

 140 fx X 90 fx, and exhibits a solid, non-medullate area of 

 cortex, marked with numerous brown spots arranged in 

 groups (fig. 16). The cortex is enclosed within a thick and 

 tangeutially stratified cuticle of clear, highly refractive 

 aspect. Examined from the side the cuticle shows the usual 

 imbricate markings. The basal part of the hair is more 

 circular in section ; it is free from the brown granules, and 

 contains only a few scattered air spaces of minute size. 



Cyclothurus didactylus. 



The two-toed ant-eater has in addition to the principal 

 hairs of the body a well-developed under-fur of much finer 

 hairs. The whole pelage is soft and fluffy. The principal 

 hairs, although much smaller than those of Tamandua, do 



