152 PROCEEDINGS OF THE ACADEMY OP [1879. 







Nineteen of these interruptions were noted; one was caused by a 

 small fly striking the snare, which the male darted at in a fierce 

 manner, but failed to seize, as the fly broke loose before he reached 

 it. Others were caused by the observer touching the foundation 

 threads or other parts of the nest. Toward the close of his ob- 

 servations he aecidently broke the suspending lines nearest to 

 him and so caused one side of the dome to fall in. This made 

 only a momentary interruption. Many of these separations were, 

 however, apparently without any extraneous cause. Twice the 

 male ran to one side of the dome, made a web attachment to a 

 bit of leaf hanging in the snare, drew out a thread about two and 

 a half inches long, which he overlaid a couple of times, and then 

 made the following motion : First, the bod} r was placed erect, i.e., 

 back upward, and was moved back and forth along the line, rub- 

 bing the points or " nippers" of the palps at the same time ; then 

 the spider swung over until the body made an angle of about 45 

 with the line, and while holding on thus the palps were rubbed 

 back and forth alternately along the line as before. The process 

 was repeated during another of the intermissions, as described 

 above. It was conjectured that the purpose of this movement 

 might be the distribution of the seminal fluid into the palpal 

 bulbs. This is taken up by the sacs, by the inflation and contrac- 

 tion of whose membranous coats it is forced into the spermathecae 

 of the female. 



May 13. 

 Wm, S. Vaux, Vice-President, in the chair. 

 Thirty-three persons present. 



The Lateral Sensory Ajiparatus of Fishes. Dr. Francis Der- 

 cum called the attention of the Academy to the so-called mucous 

 canals, or system of the lateral line in fishes. Up to the year 

 1850 these structures had been regarded as glandular, that is, as 

 secreting mucus for the purpose of lubricating the general surface 

 of the body. However, the following facts at once strike us as 

 being directly contradictory to this view. In the first place, their 

 size would render them wholly insufficient; secondly, these canals 

 are in most fishes practically closed ; and in some fishes actually 

 closed along their entire course. Again, in mollusks in which the 

 surface is equally well lubricated with those of fishes we find no 

 such structures. 



After referring to the discoveries of Franz Leydig in 1850, and 

 afterwards to the observations of F. E. Schnlze on young teliost 

 fishes, Dr. Dercum offered the following evidence in confirmation 

 of the view that these structures are sensory. Like Leydig he 

 described as occurring at regular intervals in the canals of the 

 head and lateral line certain discoidal bodies, termed by Leydig 



