84 Evolution and Distribution of Fishes 



Fig. 6. — a (to left) cerebral organ of Drepanophorus compared as an 

 auditory organ with b (to right), the young auditory organ of mammal, o, 6 

 open or closed external orifice; du. coch. ductus cochlearis ; s. u. ca. sacculo- 

 utricular canal; utr. utriculus; sac. sacculus; d. n., v. n. dorsal and ventral 

 auditory nerves; du. endo. ductus endolymphaticus. 



"In Cerebratulus, as described and figured by Burger, 

 the external orifice, the ciliated canal, the two diverticula, 

 and the distinct nerve branches seem well to correspond 

 to the ear orifice, the ciliated lymph duct, the sacculus and 

 utriculus, and the cochleo-vestibular nerves of the ear. 

 That of Drepanophorus is even more exact. Two to three 

 auditory nerves here are inserted between the two organs, 

 the sacculus and the utriculus, as in vertebrates (Fig. 6a), 

 the maculae extend along their base, while the elongated 

 process seems from position, relation, and shape to repre- 

 sent the ductus endolymphaticus. 



"If the comparison made above be correct it follows 

 that the ductus cochlearis of vertebrates and not the ductus 

 endolymphaticus, represents the primitive invagination tube 

 of the auditory organ. Further, the elongated process 

 shown for Drepanophorus in Fig. 6a suggests exact homo- 

 logy with the ductus endolymphaticus of vertebrates; 

 while Biirger's statement, that it passes backward and be- 

 comes embedded in the cellular tissue of the body, recalls 

 the often extensive ramifications of it in many freshwater 



