154 PROCEEDINGS OF THE ACADEMY OF [1879. 



membrane, were it stretched tightly, would form functionally a 

 drum-head. It is, however, quite loose, and will fluctuate readily 

 on pressure. 



The function attributed to this apparatus by F. E. Schulze, that 

 these structures appreciate mass movements of the water, and 

 also waves having longer periods than those appreciated by the 

 ear, is no doubt the correct one. However, the canals cannot act 

 in the manner suggested by Schulze, i.e., by allowing the water 

 to flow freely through them, as such a free communication with 

 the surrounding medium as is implied, is not present. As al- 

 ready stated, in some fishes the canals are completely closed along 

 their entire course, and when openings are present, they are pro- 

 bably for the purpose of maintaining an equilibrium of pressure 

 within and without the apparatus. 



The true detailed action of these organs is probably as follows : 

 Let us suppose any disturbing cause to set up a wave of long 

 period in the w r ater. It impinges, first, on the membranous inter- 

 spaces or drum-heads before spoken of, and with the greatest in- 

 tensity, of course, on those which are most nearly placed at right 

 angles to its direction. The wave is thus communicated to the 

 liquid in the canals, which transmits it to the adjacent masses of 

 jelly-like mucus covering the disks. The quivering of these 

 little masses probably excites and intensifies vibrations of the 

 hairs of the perceptive cells. The fish probably judges of the 

 direction of the disturbing cause by the portion of the apparatus 

 most intensely excited. The membranous spaces or drum-heads, 

 when the apparatus is well developed, are so arranged as to favor 

 the perception of vibrations from almost all directions. 



Dr. Dercum suggested that it would be well, in view of the con- 

 fusion existing in the present names of the dermal structures of 

 fishes, to call these organs definitely the lateral sensory apparatus 

 of fishes. This would, of course, not include the sensory ampullae 

 of the sharks and rays, nor the Savian vesicles, which have al- 

 ready distinctive names. In view of the structural resemblance 

 of the sensory disks to the maculae acusticae, he proposed to call 

 them the maculse laterales, giving a specific signification to the 

 word macula. 



May 20. 

 The President, Dr. Ruschenberger, in the chair. 

 Thirty persons present. 



Note on Mound-making Ants. Mr. McCook said that he had 

 had an opportunit}' to spend a day (June 12) on the Allegheny 

 Mountains, above Birmingham, Huntingdon Co., Pa., observing 

 the habits of Formica exsecloides, our mountain mound-builder. 

 While standing near a yellow pine tree whose roots ran into a 



