PHYLUM CHORDATA 



JEA~\ 



the cavity of the eye from the entrance of the optic 

 nerve. 



The auditory organ (Fig. 291) is chiefly distinguished 

 from that of reptiles by the great development of the cochlea. 

 The tympanic cavity and columella have the same arrange- 

 ment as in the frog ; the narrow Eustachian tubes open by 

 a common aperture (Fig.. 287, 

 eus. ap) in the roof of the 

 pharynx. 



The kidneys (Fig. 287, kd, Figs. 

 292 and 293, k) have a very 

 characteristic form. Each is a 

 flattened organ divided into three 

 main lobes and fitted closely into 

 the hollows of the pelvis. The 

 ureters (ur) are narrow tubes 

 passing directly backwards to 

 open into the middle compart- 

 ment, or the cloaca. 



The testes (Figs. 287 and 292, 

 is) are ovoid bodies, varying 

 greatly in size according to the 

 season, attached by the perito- 

 neum to the ventral surfaces of 

 the anterior ends of the kidneys. 

 From the inner border of each 

 goes off a convoluted vas def- 

 erens (yd), which passes backwards, parallel with the 

 ureter, to open into the cloaca on the extremity of a 

 small papilla. The posterior end of the spermiduct is 

 slightly enlarged to form a vesicula seminalis (v.s). The 

 female organs (Fig. 293) are remarkable for the more or 

 less complete atrophy of the right ovary and oviduct. 



Fig. 291. — Columba livia. The 

 right membranous labyrinth, 

 outer aspect; FA, ampulla of 

 posterior canal; FB, posterior 

 canal; HA, ampulla of hori- 

 zontal canal; HB, horizontal 

 canal; lag, cochlea or lagena; 

 mr, membrane of Reissner; 

 ph, basilar part of cochlea; S, 

 sacculus ; SA, ampulla of 

 anterior canal; SB, anterior 

 (canal. From Wiedersheim, af- 

 ter Hasse.) 



