230 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
1. The Removal of Sense Organs and its Effect on Equilibration. 
The normal position in which a shrimp, like Palemonetes, holds 
itself while swimming, is very characteristic : 
(a) The dorsal side of the body is always kept uppermost, its dorso- 
ventral axis corresponding to the direction of gravity, and its long axis 
usually lying in a horizontal plane. 
(6) Shrimps can be overturned only with difficulty, and even if this 
is accomplished, they right themselves at once. 
(ec) Animals coming to rest upon surfaces not horizontal tend to 
keep themselves in the horizontal plane, but with the dorsal side 
always up. 
a. Eyes blinded. Nearly fifty animals were operated upon in this 
way and their movements observed. Placed in an aquarium, they swam 
about indiscriminately, but always with the dorsal side up, there being 
little if any rolling from side to side. They were not easily overturned 
artificially, and when interfered with, righted themselves quickly. The 
most noticeable difference to be observed between their mcevements 
and those of normal animals was the tendency to remain quiet and 
to hold fast to any object with which they came into contact, thus 
substituting the sense of touch for that of vision lost. It is apparent, 
therefore, that some organ or organs other than the eyes play the chief 
part in equilibration. 
b. Both Otocysts removed. Twenty-five animals were operated upon 
by removing both otocysts. In swimming there was still a strong 
tendency to keep the dorsal side uppermost, but there was in every 
case marked rolling from side to side, which occasionally culminated 
in a complete rotation about the long axis of the body. The animals 
could be easily overturned, and though they strove to right themselves, 
it was not accomplished as soon nor as accurately as in normal or blinded 
shrimps. They were more apt to remain quiet, or to swim along upon 
the bottom of the aquarium, than to swim free. If the long flagella 
of the first and second antenne were removed, rolling motions were 
increased and also the difficulty in righting themselves if overturned, 
the flagella being probably used ag balancing organs in equilibration ; 
but the extirpation of the otocysts alone brings about a marked loss of 
orientation, much more pronounced than that produced by simply 
blinding. 
c. Both Eyes blinded and both Otocysts removed. Upon removal 
of both otocysts and blinding of both eyes, entire loss of the normal 
