Contributions to the Histology of Brady pus tridactylus. 45 
The Organs of Respiration. 
The sloth lives a sluggish life in hot climates, so there is no 
necessity to warm the air during the process of respiration. 
The larynx is lined by cubical cells, but the vocal cords are 
clothed with stratified epithelium. 
The pulmonary alveoli (text-fig. 11) are large, so the prepara- 
tion of satisfactory sections is a matter of considerable difficulty. 
Many of the sacs intercommunicate, but I believe that the septa 
Text-Fig. 12. — Algge on the hairs. The large ones are green, 
and the small ones are pink. 
have been broken down in the process of preparation. In some 
parts fewer than twelve alveoli fill the field. They vary greatly 
in shape, but the majority are long, narrow and irregular, or small 
and circular according to the plane of section. They are lined by 
large cubical cells containing one or more nuclei, and possessing 
granular protoplasm. Their blood-vessels are thin walled and 
capacious, and some, which are cut longitudinally, appear as 
irregular tubes packed with red blood corpuscles. 
Text-Fig. 13. — A hair-shaft with algee. 
The bronchi have well-developed muscular coats, and there is 
a large amount of connective and elastic tissue around them. 
The appearance of a section through the lung of the sloth is 
very like that of vesicular emphysema in man. 
ON THE MICROSCOPIC STRUCTURE OF THE HAIR OF 
BRADYPUS TRIDACTYLUS. 
(Text-figs. 12 and 13.) 
The body of B. tridactylus is clothed with long, stout, somewhat 
brittle hairs forming the “ outer ” coat, and finer, soft, short “ fur ” 
