the lateral line organs, 25 



Section 2. — The Lateral Line Canals and their 

 Organs, 



The problems of the relations and significance of the 

 sensory nerve components are so intimately bound up 

 with those of the cutaneous sense organs innervated by 

 them that an account of these organs must naturally pre- 

 cede the discussion of the nerves themselves. I have 

 prepared in this section as complete an account as possible 

 with the material at hand of the structure of the special 

 cutaneous sense organs belonging to the lateral line 

 system of the adult Menidia. There is urgent demand 

 for very careful study of the comparative embry- 

 ology of the various t3^pes of lateral line organs and 

 terminal buds. The data thus far furnished by the em- 

 br}^ologists are very "suggestive," but what they suggest 

 must for the most part remain a matter of dispute so long 

 as the ultimate fate of their so-called sense organs remains 

 unknown. 



I. — The Lateral Lines. 



There is probably no teleostean character which is more 

 variable in its details than the lateral line canals. In 

 Menidia we find the system so developed as to conform 

 very nearly to what is usually regarded as the typical 

 form, such as is given by AUis in his diagram ('89, Plate 

 XLII) of Amia one month old or by Cole of the adult cod 

 ('98a, Fig. 2). If we compare with these diagrams my 

 reconstruction of the adult Menidia on Figs. 3 and 5, the 

 resemblance is close, the chief difference being the failure 

 in the case of Menidia of the canals to close over the rows 

 of lateral line organs throughout their entire extent. 

 Thus the rows of organs are present in their typical re- 

 lations, but the canals are in places interrupted. 



