2 28 CLAP P. [Vol. XV. 



open groove in the bone (Fig. 5). The succeeding organs, 

 5-7, are within a canal in the articular bone (Fig. 5). At the 

 angle of the jaw the opercular division begins, and consists of 

 four enclosed organs (8-1 1) with one (12) free organ near the 

 temporal region (Fig. 22). Outside of these twelve organs of 

 the operculo-mandibular line there are accessory lines of free 

 organs. On the mandible there is a short line of three organs 

 (PL XVII, Fig. 3, ac.md.l.) anterior and parallel to the canal. 

 Near the pore at the junction of the two portions of the 

 operculo-mandibular line there are two free organs {mdl.) (Figs. 

 I, 3, and 22), while on the operculum two lines of free organs 

 diverge at right angles to the canal in the preoperculum, the 

 more dorsal (d.o.l.) having four, and the other (v.o./.) three 

 organs (Fig. 22). 



4. Body lines. — There are three lines of free organs on the 

 side of the body (Fig. 24) ; the most dorsal, of twenty-seven 

 organs, being a continuation of the infraorbital, the middle line 

 appearing as a branch from this line, represented by only a few 

 scattered organs, usually eleven, and the ventral line, of twenty- 

 seven organs, extending from a point in front of the ventral 

 along the border of the anal fin. Continuations of these lines 

 are found on the caudal fin, but the organs are somewhat 

 diminished in size toward the posterior end of the body. The 

 usual number on the caudal fin is four. 



Canals. 



The canals enclosing lateral line organs are found only on 

 the head, and these present a rudimentary, perhaps vestigial 

 condition in Batrachus. 



From Fig. 22 it appears that the infraorbital line through- 

 out its extent has only two short canals, one on the maxillary 

 branch containing two organs, and the other in the temporal 

 region enclosing only one. The supraorbital line, on the other 

 hand, exhibits the opposite condition, in that all the organs of 

 the line are enclosed in a canal with the exception of a free 

 organ at each end of the line. The operculo-mandibular canal 

 is well developed, only five of the twelve organs being super- 



