230 BULLETIN : MUSEUM OF COMPAKATIVE ZOOLOGY. 



1. The Removal of Sense Organs and its Effect on Equilibration. 



The normal position in which a shrimp, like Palasmonetes, holds 

 itself while swimming, is very characteristic : 



(a) The dorsal side of the body is always kept uppermost, its dorso- 

 veutral axis corresponding to the direction of gravity, and its long axis 

 usually lying in a horizontal plane. 



(b) Shrimps can be overturned only with difficulty, and even if this 

 is accomplished, they right themselves at once. 



(c) Animals coming to rest upon surfiices not horizontal tend to 

 keep themselves in the horizontal plane, but with the dorsal side 

 always up. 



a. Eyes blitided. 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 movements 

 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 Otocysfs 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 qiiiet, or to swim along upon 

 the bottom of the aquarium, than to swim free. If the long flagella 

 of the first and second antennae were removed, rolling motions were 

 increased and also the difficulty in righting themselves if overturned, 

 the flagella being probably used as 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 



