BULLETIN OF THE UNITED STATES FISH COMMISSION. 7 



The dcvclopnieut of the median lins of BatracJms is more direct than 

 usual in young- fishes; that is to say, the atrophy of certain portions of 

 the fold are not extensive, because the median fins of the adult are al- 

 most continuous. 



The larval integument, when sections of it are prepared, is shown to 

 be ver}- thickly covered with muciparous unicellular glands, similar to 

 those observed in the salmon. 



The lateral line system is very well developed and begins to show 

 itself very distinctly before the embryo is half an inch in length. The 

 portions continued over the head and lower jaw remain open until the 

 young fish is about a half-inch in length ; after that the edges of what 

 were open grooves coalesce and in that way the closed canals over the 

 head are formed. At short intervals, however, the edges of the grooves 

 do not close, and these open spaces in the outer walls of the mucoder- 

 mal or neuromastic canals form the pores which open into the lateral 

 line system from the outside. 



This system is not, as is usually the case in other fishes, i)rolonged 

 backwards on either side of the body and tail of the Toad-fish as a single 

 canal, but divides behind the hyomandibular into a ventral and a dorsal 

 canal, each of which passes along nearly parallel close to the base of 

 the dorsal and anal fins respectively. The upper one of these canals 

 passes along above the insertion of the pectoral, and the lower one 

 passes below the base of that fin. 



In the adult the pores which open outwards from the system of lat- 

 eral canals are not simple openings without defense of any sort; on the 

 contrary, those on the head, body, and tail are always defended by a 

 pair of strongly-developed papillaB, which almost comi)letely conceal 

 the pore opening between their bases. On the body one of the papillae 

 arises below the i^ore and another above it. These paired papillte are 

 best developed on the head and jaws, and they gradually become more 

 and more rudimentary towards the tail. No evidence of the develop- 

 ment of these i)apill8e can be found on any of the later larval stages in 

 my possession, so that it is obvious that they are of post-larval origin. 

 The anterior uareal opening in the embryo of BatracJms is quite near 

 the middle line, and is produced into a tubular prolongation before the 

 young fish reaches the length of one-half inch. The posterior nareal 

 opening, on the contrary, is a simple pore, and stands farther from the 

 middle line than the anterior one. 



Judging from the highly specialized character of the lateral line sys- 

 tem of canals in Batrachus, and the pores^onnecting canals, papillae, and 

 nerves which pass to the apparatus, it is obvious that the latter is quite 

 complex and must subserve some very important function. That its 

 sole function is to secrete mucus is absurd on its own face, even if we 

 had no direct experimental evidence to show that these organs are the 

 instruments of a special sense. In mounted preparations of the skin 

 of the larvae, prepared for me by Professor Libbey, it may readily \)e 



