VOCAL GROANS OF MAMMALS. 569 



while the female is fawn-colored : male antelopes are blacker 

 than the female. The Banteng bull is almost black, while 

 the cow is of a bright dun. Among the lemurs the male of 

 Lemur macaco is coal-black, while the female is reddish yel- 

 low. The sexes of monkeys differ much in coloration. Cer- 

 tain male seals, bats, rats, and squirrels have brighter colors 

 than in the opposite sex. On the other hand, the female 

 Rhesus monkey is adorned with a brilliant red naked ring 

 around the tail ; this is wanting in the male, which, how- 

 ever, is larger, with larger canines, more bushy whiskers 

 and eyebrows ; and Darwin states that in monkeys the males 

 usually differ from the females in " the development of the 

 beard, whiskers, and mane." 



The vocal organs of mammals are, in general, constructed 

 on the same type. The larynx is formed by a modification 

 of the uppermost ring of the trachea, called the cricoid car- 

 tilage, to the anterior and dorsal edges of which two arytenoid 

 cartilages are attached, while a V-shaped thyroid cartilage, 

 open behind, is attached to its side. The vocal cords, which 

 are modified folds of the mucous membrane lining the 

 trachea, are stretched between the arytenoid and thyroid 

 cartilages, the slit between them being called the glottis, 

 which is covered by the epiglottis. Thus, in mammals the 

 organs of voice are situated almost solely at the upper end 

 of the trachea. In the whales the vocal chords are not de- 

 veloped. The male gorilla, which has an exceedingly loud 

 voice, as well as the adult male orang and the gibbon, is 

 provided with a laryngeal sac. In the howling monkey 

 (Mycetes) of Brazil, the hyoid apparatus and larynx are re- 

 markably modified, the body of the former being changed 

 into a large bony drum or air-sac communicating with the 

 larynx. The vocal organs are a third larger in the males 

 than in the females. " The males begin the dreadful con- 

 cert, in which the females, with their less powerful voices, 

 sometimes join, and which is often continued during many 

 hours " (Darwin). They apparently howl, as birds sing, 

 for the simple pleasure of the thing. Apparently, the most 

 musical mammal, man excepted, is a gibbon (Hylobates 

 agilis), which can sing " a complete and correct octave of 



