L. J. THOMAS. 



expanded to about 0.043 mni - Two nuclei of apparently fixed 

 relationships are found in the secondary pedicel, one near the 

 proximal and the other near the distal end. 



The cavity of the secondary vesicle is normally spherical in 

 form though it is capable of some distortion. The diameter is 

 about 0.138 mm. The contents of this cavity take stains so 

 lightly and so evenly that there is strong evidence that only a 

 fluid is present. Two or three concentric rings are observable in 

 the spherical otolith contained within the secondary vesicle (Figs. 

 4-5, Plate I.). There is considerable variability in the size of 

 the otolith. Some of the largest measured 0.069 mm - m diameter. 

 The fluid in which the specimens were preserved was distinctly 

 acid, consequently any calcareous deposits that might have been 

 present in the otolith had been destroyed, leaving only the sup- 

 porting structures. Perkins (1902: 786) refers to the otolith as 

 " a calcium salt deposit in an organic matrix." In the specimens 

 examined the otolith had no fixed position within the secondary 

 vesicle but was apparently free to move about in the fluid filled 

 space. The entire sensory mechanism as ordinarily described for 

 an otocyst is thus contained within the confines of the spheroid. 

 In the light of this morphological evidence it might be easily pos- 

 sible that the destruction of the primary vesicle need not appre- 

 ciably impair the functioning of the organ. 



Murbach (1903: 206) in experiments upon the function of the 

 otocysts of Gonioncmus collapsed the " otocysts " by thrusting 

 them with a fine needle. In all probability the injury inflicted 

 did not extend beyond the collapsing of the primary vesicle. Ac- 

 cording to his statements the specimens continued to act normally 

 after this treatment. Upon the results of these experiments and 

 upon the behavior of a single individual from which the otocysts 

 were excised he based his conclusion that the otocysts play no 

 important part in establishing the equilibrium in Gonionemus. 

 The more or less normal behavior of the much mutilated indi- 

 vidual from which the otocysts were cut is not readily explain- 

 able. On the other hand, in view of the fact that morphologically 

 the entire sensory mechanism of the otocyst seems to be confined 

 to the secondary vesicle there is little reason to expect serious 



