466 THE DOGFISH CHAP. 



capsule, is often spoken of as the internal ear. In the frog 

 there is also an accessory apparatus the tympanic cavity 

 and membrane, together with the columella which is 

 called the middle ear (compare Fig. 10 and pp. 189 and 449). 



Urinogenital organs. The kidneys of the dogfish are 

 narrow, lobulated organs, lying close to the vertebral 

 column on either side and covered ventrally by the thick 

 peritoneum. They extend primarily along almost the 

 whole length of the ccelome, but in the course of 

 development (see p. 601) certain important modifica- 

 tions take place in them and their ducts. 



It will be remembered that in the male frog the efferent 

 ducts from each spermary enter the comparatively 

 short kidney of the same side, and that the duct of the 

 latter serves as a urinogenital duct (p. 193). In the 

 dogfish, about the anterior half of the primary kidney 

 loses its excretory function (Fig. 127, k', k") ; in the 

 male it becomes connected with the anterior end of the 

 spermary by means of a small number of fine efferent 

 ducts (ef. d) and gives rise to a glandular body, the 

 so-called cpididyvnis (A, k', k"), through which the sperms 

 pass in order to reach the original kidney-duct, which 

 serves as a spermiduct only (spd) . This duct remains in 

 close connection with the epididymis ventrally and 

 becomes greatly convoluted. In the female the whole of 

 the anterior part of the primary kidney and its duct 

 are merely represented by vestiges (B, k'). The 

 posterior half of the embryonic kidney in each sex is the 

 only part which serves as a renal organ ; this is some- 

 what swollen posteriorly, and in connection with it 

 special ducts or ureters are developed to carry off the 

 urine (ur). In the female these open separately into 

 the persistent posterior ends of the primary kidney- 

 ducts, which unite together at their bases to form a 

 median urinary sinus (B, u. s), opening by a single 



