112 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Both the male and the female Labidocerse, after the rough handling incident on 
being squirted several times from a pipette into a vessel of sea water, still showed 
unchanged their characteristic geotropic responses; and even after they had been 
violently shaken in a test tube partly filled with sea water no alteration in their 
geotropism was observed. Mechanical stimulation, therefore, seemed insufficient to 
change their reactions to gravity. This accords with what was observed on the 
surface of the sea, for at night Labidocerse were often as abundantly obtained when 
the sea was rough as when it was smooth. 
Changes in density were next tried. Sea water of a specific gravity 1.025 was 
filtered, concentrated by boiling, cooled, and aerated, and then diluted with distilled 
water till the requisite densities were obtained. Females introduced into waters of 
specific gravities 1.050 and 1.035 retained their negative geotropism and showed no 
differences from normal animals except that they moved more frequently by leaps. 
Males when placed in similar concentrations frequented the upper portion of the 
vessel more generally, i. e., had their negative geotropism somewhat increased, and 
leaped more frequently. Concentrated sea water then induced leaping movements in 
both sexes, increased slightly the negative geotropism of the males, without, however, 
making any noticeable change in the geotropism of the females. 
In sea water of less density than the normal, the reactions of the males and the 
females, unless otherwise stated, were similar, and the following records apply to 
both sexes. In sea water diluted from 1.025 to 1.020 the animals darted about when 
first introduced and then gradually became distributed as was usual, the females near 
the top and the males scattered. In water of the specific gravity 1.015 the animals 
introduced darted about vigorously, after which some went to the bottom, 50 centi- 
meters distant, and some remained above. In water of a specific gravity 1.010 all 
animals exhibited darting movements and went to the bottom in irregular spirals. 
They were left in the mixture, and all died in the interval between a half hour and 
an hour after introduction. In water of a specific gravity 1.005 all fell rapidly, 
each making one or two leaps and reaching the bottom apparently dead. In pure 
Water the animals made one or two leaps, and were dead before they reached the 
bottom. The effect of diluting the sea water did not seem in any case to change 
geotropic responses. Slight dilution stimulated the Labidocerse to leaping, and 
greater dilutions, after stimulating them to a few leaps, rendered their movements 
incoordinate, so that they fell to the bottom without showing responses which at any 
time could have been interpreted as a change in the sense of their geotropism. 
When ordinary sea water was covered by an inch or so of sea water diluted to a 
specific gravity 1.015 and Labidocerse were liberated at the surface, they almost 
always sank with a few violent leaps till they entered the ordinary sea water, 
whereupon they became normally distributed, in that most of the males dispersed 
and the females congregated near the upper surface, not of the water as a whole, but 
of the normal sea water. 
This experiment indicates that under natural conditions even excessive rain is 
not likely to change essentially the distribution of Labidocerse, for they would at 
most be driven only a few inches from the surface. Dropping fresh water into a 
tube of sea water containing female Labidocerse, so that in the course of about an 
hour the level of the tube rose a centimeter, could not be said to have driven the 
animals from the surface, though they occupied a somewhat deeper position at the 
