xii 



PHYLUM CHORDATA 



481 



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. 



T\& kidneys (Fig. 287,^, 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 ^tr) are narrow tubes 

 passing directly backwards to 

 open into the middle compart- 

 ment, or the cloaca. 



The testes (Figs. 287 and 292, FIG. 291. Coiumba livia. The 



right membranous labyrinth, 



is) are ovoid bodies, varying outer aspect; FA, ampulla of 



. posterior canal; FB, posterior 



greatly 111 Size according tO the canal; HA, ampulla of hori- 



zontal canal; HB, horizontal 



season, attached by the pento- 



canal; Ing, 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.) 



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 (vd), 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. 

 21 



