vol. i.] Bitter-Davis. — Enteropneusta . L93 



proportional to the viscosity of the liquid in which the organism 

 moves. Viscosity increases at the rate of about two per cent. 

 for each degree of rise in temperature and also with the density 

 of the medium through dissolved salts. In some cases where 

 temperature and rate of sinking were noted we found this theo- 

 retical conclusion as to the influence of viscosity in a measure 

 confirmed, e.g., at 16° C the rate of sinking was 3.65 mm. per 

 second; at 20° C 4.77 mm. per second; at 22° C 5.05 mm. pet- 

 second. These averages are confirmatory to the extent that they 

 show an increase in rate with increase in temperature, but the 

 increase is above the theoretical amount of even three per cent, 

 for each degree of temperature. The following tabulation of 

 some of our typical results shows a still greater discrepancy 

 between the actual and theoretical relation of temperature and 

 viscosity: 



Although these trials were made for another purpose, the 

 conditions as to specific gravity and form resistance were con- 

 stant enough to give the theory a rough test. A much larger 

 number of observations with special care in controlling other 

 variables will be needed to reach any definite conclusion as to the 

 reaction of viscosity on rate of sinking. 



What now, we may inquire, is the stimulus or other 

 immediate influence that leads to the upward migration of the 

 larva? Several possibilities suggest themselves. Pressure of 

 the water, greater at the bottom where the eggs are hatched, and 

 diminishing gradually to the surface, might be a factor in the 

 case; or the presumably increasing oxygen content of the water 

 from the depth upward may lie the determining element. Again, 

 the higher temperatures of the upper strata of water, acting 

 directly on the organism or through the thereby diminished 

 viscosity, the matter to which Ostwald has drawn attention, 

 might be the sole or most potent factor. 



We have no experimental evidence of our own, nor do we 

 know of any produced by other investigators, upon which to base 



