208 



ZOOLOGY 



SECT. 



cp. n-a, L 



ch. gld, choroid gland ; en. cornea ; cp. hal. cam- 



panula Halleri; ir iris ; /. lens; opt. m>. optic towards, 



nerve ; pg. pigmentary layer ; pr. fl. processus , ' 



faiciformis ; sci. sclerotic (dotted). drawn trom, the retina. 



or 



efferent artery of the pseudobranch. Close to the entrance of the 

 optic nerve a vascular fold of the choroid, the falciform process 

 (pr. //.), pierces the retina, and is continued to the back of the lens, 

 where it ends in a knob, the campanula Halleri (cp. hal.), which 



contains smooth muscular 

 fibres. The falciform pro- 

 cess with the campanula 

 Halleri takes an important 

 part in the process of accom- 

 modation by which the eye 

 becomes adapted to forming 

 and receiving images ^f 

 objects at various distances. 

 Accommodation in the Bony 

 Fish is effected, not by an 

 alteration in the curvature 

 of the lens as in higher 

 Vertebrates, but by changes 



FIG. 878. Salmo fario. Vertical section of eye in its position, by which it 

 (semi-diagrammatic), arg. argentea ; ch. choroid ; becomes more approximated 



further with- 

 in 



bringing about these changes 



of position the structures in question appear to play the principal 

 part. 



The auditory organ (Fig. 879) is chiefly remarkable for the large 

 size of the otoliths (ot. 1). They are three in number ; one, 

 called the sagitta (ot. 7), is fully 6 mm. in length, and almost fills 

 the sacculus : another, the asteriscus (ot. 2), is a small granule lying 

 in the lagena or rudimentary cochlea : the third, the lapillus (ot. 3), 

 is placed in the utriculus close to the ampullae of the anterior and 

 horizontal canals. 



Urinogenital Organs. The kidneys (Fig. 876, kd., and Fig. 

 880, R) are of great size, extending the whole length of the dorsal 

 wall of the abdomen, above the air-bladder, and partly fused 

 together in the middle line. They are derived from the meso- 

 nephros of the embryo. Their anterior ends (Fig. 876, kd, Fig. 

 880, R) are much dilated and consist in the adult of lymphatic 

 tissue, thus ceasing to discharge a renal function. The ureters 

 (mesonephric ducts, ur.) unite into a single tube, which is dilated 

 to form a urinary bladder (Fig. 876, u. bl., Fig. 880, v.), and discharges 

 into the urinogenital sinus. 



The gonads are of great size in the sexually mature fish. The 

 testes (Fig. 876, ts.) are long, smooth, pinkish paired organs, extend- 

 ing the whole length of the abdominal cavity ; each is continued 

 posteriorly into a duct (v. df.) which opens into the urinogenital 

 sinus, and the homology of which with the ducts of the primitive 



