734 



Ganoids (Chondrostei and Holoatei) is likewise overgrown by the 

 cartilaginous auditory capsule, and of which (ram. oticus) it was 

 known that it sends out brandies in this region to the sense organs, 

 belonging to the lateral line system. 



These sense organs, called neiiromasts (Nerveiihiigel) by Wright, 

 lie either free on the surface, or protected in little sacs, grooves 

 or canals; all are of ectodermal derixalion. Now it was noteworthy 

 that the sense organ of the spiraciilar pouch also resembled the 

 structure of a neuromast, although Wkight evidently thought it to 

 be of entodermal origin. It seemed as if one here had the unexpected 

 example of a sense organ of the Chordates, which did not originate 

 from the ectoderm, although it was still supplied by a nerve, 

 belonging to the lateral line system of the epidermal sense organs. 



The study of the Dipnoi dispelled the singularity of this pheno- 

 menon. In this group Pinkus (1895) discovered in Frolopterus 

 annectens a little bladder with a sense organ on its wall, and 

 imbedded in the cartilage of the otic region. The sense organ — 

 evidently a neuromast according to the fig. — is supplied by a 

 caudalwards running branch of the facial nerve, the branch 

 belonging to the lateral line system. 



Pinkos still describes two more caudalwards running branches 

 from the lateral line system of the n. facialis. The one forms the 

 well known anastomosis with the ramus lateralis vagi (and glosso- 

 pharyngei) the other he calls ram. oticus. He, however, draws the 

 origin (I.e. fig. 3) of these branches so close to each other that, 

 according to my opinion, one has to consider them as the strongly 

 developed homologne of the ram. oticus of the (lanoids. 



Of this organ Pinkus says (I.e. p. 307) "Das Organ ist zweifellos 

 ein Derival des Seitenkanales. Ueber seine Bedeiitung vermag ich 

 iibrigens nichts auszusagen, da \ergleicliend analoinische und ent- 

 wicklungsgeschichtliclie Tliatsadien inir bisher fehlen". 



For Ihe knowledge of the development we are indebted lo Agar, 

 (1906) who examined the first stages of the spiraculum in Lepi- 

 dosiren and Protopterus. 



He showed that this sense organ is of ectodermal origin. This 

 seat of origin reaches the top of the solid gui proluberance, which 

 represents the spiracle, and then sever.s itself from the ectoderm. 

 The organ then naturally gives the impression of having been derived 

 from the entoderm. 



Agar like Pinkus, was not aware of Ihe work of Ramsay Wright, 

 otherwise he would undoubtedly have mentioned, that the presence 

 of a spiraciilar sense organ in Holoslei was already known. He also 



