318 RESEARCH SEMINAR. 



were made to change the center of gravity by weights, etc. 

 These were followed by the removal of different organs, the 

 tentacles, tfie manubrium and the gonads, but without producing 

 any marked disorientation. It seemed, then, that the otocyst 

 organs to which this function is usually ascribed were thus shown 

 to be active. 



At first, solution of the otoliths was attempted with various 

 acids ; but it was found that all acids tried, if strong enough to 

 dissolve the otoliths, also killed the animals. Then the vesicles 

 were punctured, putting the otocysts out of function, but in the 

 light of all the experiments there was no definite disorientation, 

 except when the velum was severely mutilated. While this was 

 not a proof that the otocyst organs do not function as the principal 

 organs of equilibrium, the latter observation suggested that equi- 

 libration in this medusa is, to a large extent, to be ascribed to 

 " muscular sensation." Further experiments were finally made, 

 cutting away the margin of the bell, including the bases of the 

 tentacles and the otocyst organs. Intermediate portions of the 

 margin were left until healing had taken place ; then the remain- 

 ing portions of the margin were cut away and the a*nimal tested. 

 Although the medusa was more or less imperfect from the opera- 

 tion it was not seriously disoriented but moved in definite direc- 

 tions, including swimming to the surface of a shallow dish of 

 sea water and turning over, also lying with the opening of the 

 bell turned up. 



From all the experiments it seems to follow that the otocyst 

 organs serve very little in the equilibrium of the medusae, and 

 that the muscular sensation is probably the principal factor. 



August 7. Nestling and Juvenile Plumages of Sterna hirundo 

 and S. dougalli. By LYNDS JONES. 



The ventral downs of the nestling plumage are wholly white, 

 except the throat, where the tips are dusky-black. All dorsal 

 downs have a dusky-black base, then a tawny area, then a 

 dusky-black area, and many a tawny tip. In the nestling hii- 

 undo these dusky tips are arranged in mottled pattern, but in 

 dougalli in stripes. Both patterns are protective, dougalli nest- 

 ing mostly among grasses, hirundo originally on the beach 

 among pebbles and seaweed. 



