228 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



tion resulting from long confinement and low temperature. Moreover, 

 the operation was one of some difficulty, because of the necessity of 

 cutting through the bony skull. 



1. Material. 



In the summer of 1900, while occupying at the U. S. Fish Commission 

 at Wood's Hole one of the tables assigned by the Museum of Comparative 

 Zoology, I had, through the courtesy of Dr. Bumpus, the director, the 

 opportunity of conducting some successful experiments upon selachians. 

 The animals used were of four species, the dusky shark (Carcharhinus 

 obscurus), the sand shark (Charcliarias littoralis), the spiny dog-fish 

 (Squalus acanthias), and the smooth dog-fish (Mustelus canis). These 

 animals are, for a number of reasons, particularly favorable subjects 

 for this experiment. 



2. Method of Operation. 



In sharks Reissnei-'s fibre is of relatively large size, from 8 to 20 

 micra in diameter, and in passing through the fourth ventricle into the 

 central canal is at some distance above its floor. As a preliminary ex- 

 periment, I took tlie brain and anterior portion of the spinal cord from a 

 small shark, and attempted to draw out Reissuer's fibre. Opening the 

 fourth ventricle I took a fine needle, curved into a microscopic hook at 

 its tip, and drew it transversely across the floor of the ventricle, until I 

 had caught the fibre and could lift it free from the cerebro-spinal fluid. 

 It was not until after many failures with successive brains that I was 

 able to do this. • I also succeeded in drawing the fibre out of the central 

 canal. Taking a freshly cut section of the cord 1 to 2 inches long, 

 I was able, after many trials, to seize the fibre with fine tweezers and 

 draw it from the canal. The fibre when thus withdrawn is perfectly 

 transparent, and many times finer than the finest hair, but may be readily 

 seen in a strong light because of its high refractivity. It is somewhat 

 elastic, contracting after being stretched. It has also a considerable 

 degree of tenacity, so that in a number of cases I was able to stretch it 

 across a glass slide. In this way I studied microscopically the freshly 

 isolated fibre with the aid of methylen blue, and also made some 

 permanent preparations of it. 



The operation of cutting the fibre is simple and easy. A small. shark 

 three to four feet long was taken from the floating cage in which 

 the animals were kept, and quickly placed on the operating table. 

 By means of a rubber tube 1 to 2 inches in diameter, placed in its 



