MUSEUM OF COMPARATIVE ZOOLOGY. Ill 



''1, als verzweigte Eohren, die in oder unter der Haut liegen. Sie setzen 

 zusanimen das System der Seitenlinie also die Seitenlinie selbst und ihre 

 Auslaufer ; 



"2, als nicht verzweigte Rohren, welche iiiit einer erweiterung — Ampulle 

 — blind geschlossen beginnen und sich auf der ausseren Haut ofFnen ; 



" 3, als geschlossene Blasen, die also nioht iu der Haut ausmiinden. 



"Mit der ersten und zweiten Classe sind siimmtliche Rochen und Haie ver- 

 sehen, rait der ersten, zweiten und dritten zusammen bloss die Zitterrochen." 



KoUiker, 1856 and 1858, and Max Schultze, 1862, showed the exist- 

 ence of a sensitive epithelium within the follicles. 



Leydig, 1868, brought forward one of the most important contribu- 

 tions to knowledge of the organs under consideration. It was entitled 

 " Ueber Organe eines sechsten Sinnes," and it deals with the matter in 

 the most compi'ehensive way. The three classes of vessels are accepted 

 as organs of a sixth sense. 



Boll's monograph, " Die Lorenzinischen Ampulleu der Selachier," 

 appeared in the same year, 1868. As its name indicates, it was devoted 

 to the ducts, but references to the canals are included. 



A valuable addition to the literature, and very exhaustive so far as 

 the follicles themselves are concerned, is the monograph, " Le vesicole di 

 Savi della Torpedine," 1875, by the same author. He is able in this 

 work to give no additional light on the physiological function of the 

 vesicles. The idea that they are a form of the canals has little in it 

 that is seductive to him, since it involves, as he says, asci'ibing one 

 office to two organs of very different structure in the Selachia generally, 

 or to three diverse organs in the Torpedinidte alone. The hypothesis of 

 R. Wagner, that the follicles provoked, in reflex manner, the activity of 

 the electric organ, he claims to have shown in 1873 to be without foun- 

 dation ; and he maintains that the opinion that the follicles of Savi 

 represent an organ of electric sense may only be discussed when the 

 presence or absence of analogous organs is established in the other 

 electric fishes. 



To Balfour, 1878 and 1881, more perhaps than to any other one, we 

 are indebted for knowledge of the origin and innervation of the canals. 

 He first found the lateral nerve to originate as the other nerves, and to 

 push backward, following the lead of the canal and sending branches to 

 connect with it in the successive segments that were traversed. His 

 conclusions disagreed with those of Semper and Goette, who claim that 

 the lateral nerve originates directly from the epiblast of the lateral 

 line, but the results of more recent study favor his opinions rather 

 than theirs. 



