SPECIES ALLIED TO MOTELLA. 31 



The observations of Malbranc* and Beard, according to which more than 

 one pair of these organs may occur in a single segment as the result of a 

 division of a primary pair, we have not been able to confirm. We have seen 

 cases in which there were apparently two of these organs in close proximity, 

 neither of which was perfectly developed. In no case have we found two 

 well developed side by side. The occurrence of three lateral lines in some 

 Flounders, and the occurrence of the same number, as a rule (Malbranc), in 

 Amphibians, is not easily explained as a result of the division of one line, but 

 is precisely what might be expected if the view above suggested is correct. 

 The same view would also offer a ready explanation of the position of these 

 organs at different heights, as shown in the species here described. The 

 sense-organs of the body and tail represent three series, which we may 

 designate as dorsal, ventral, and intermediate. The dorsal and ventral series 

 are each represented by a single organ, while the intermediate is represented 

 by from two to three. The dorsal and ventral series are developed in the 

 middle region of the trunk, and the intermediate series only on the tail. Pre- 

 cisely the same arrangement is seen in Fierasfer.f A comparison of our figure 

 and that of Emery with Malbranc's Plate I., Fig. 10, representing a young 

 Axolotl, will show that the view above presented is not without support. 



There are undoubtedly more than one series represented in the lateral- 

 line organs of the head ; but here the arrangement gives no clue to the 

 precise number of series. 



Although we have seen no direct evidence of a multiplication by division 

 among these organs from the studies of Malbranc on Amphibia, such a mode 

 of development is very probable. But allowing this to be true, it is evident 

 that it does not offer a satisfactory explanation of the presence of three or 

 more distinct segmental series ; and it accords quite as well with the view 

 that there were originally several series of lateraMine organs, as with the 

 commonly received opinion that there was but one series. 



The important discovery made by Mayser,$ that the nervus lateralis vagi 

 (Stannius) is composed of two kinds of fibres, representing the recurrens 

 superior and the posterior root of the acusticus (N. VIII. post), goes far 

 towards deciding the question of the function of the lateral-line organs as 



* Malbranc, M. " Von der Seitenlinie and ihren Sianesorganen bei A.mphibien," Zeitschr. f. wiss. 

 Zool., XXVI., pp. 76-80. 



f Emery, Carlo. Fauna uml Flora rles Oolfcs von Neapel. 11. Monographic: Fierasfer. (Fig. IX. 

 p. 43.) 1S80. 



X Mayser, P. " Vergl. anal. Studien lib. d. Geuirn d. Knochenfische, ' Zeitschr. f. wiss. Zool., XXXVI. , 

 1881, pp. 309-311. 



