BOTRYLLUS SCHLOSSERI (PALLAS). 225 



sible that the eel grass might give off some substance to which the 

 Botrylhis larva orients. The result of one experiment, however, 

 indicated plainly that this was not the case. Clean blades of eel 

 grass were stretched between the ends of a piece of coarse wire 

 netting, bent into the shape of a flat U. The blades were so ar- 

 ranged that their flat surfaces were parallel to the central portion 

 of the wire netting. This apparatus was suspended near the 

 bottom of a large aquarium at the least illuminated side. The 

 only source of light was an opening in the covering of a north 

 window of approximately the same size as the aquarium. Since 

 the aquarium stood immediately in front of this opening, the in- 

 tensity of the light on the two sides of the eel grass blades was 

 practically the same, and the possibility of light intensity playing 

 any part in determining the location of the larvae on the eel grass 

 was thus largely eliminated. Larvae were introduced into the 

 aquarium immediately after liberation from the parent colony, 

 and were allowed to metamorphose there. When sufficient time 

 had elapsed for attachment to have taken place, records were made 

 of the location of the zooids. It was expected that if the eel 

 grass gives off a chemical substance to which the larva orients, 

 at the time when metamorphic changes are about to begin, the 

 metamorphosing zooids would be found on the eel grass. Al- 

 though larvae had been observed to swim about the grass blades, 

 not one metamorphosing zooid of the several hundred in the 

 aquarium, was found attached to them. This result indicates 

 plainly that chemical attraction is not a factor in determining the 

 place of attachment of the larvae for metamorphosis. 



Response to Gravity and Light at the End of the Free-swim- 

 ming Period. In the experiments first described in which larvae 

 were allowed to metamorphose in crystallization dishes containing 

 blades of eel grass stretched from the bottom of one side to the 

 top of the other the factor of gravity would have but a small part 

 in determining the place of metamorphosis of the zooid because 

 of the shallowness of the water. It seemed as if in its natural 

 habitat, a positive response of the larva to gravity at the time of 

 metamorphosis would be advantageous, since it would tend to 

 bring the larva into contact with a place suitable for metamor- 

 phosis, such as the lower portion of eel grass blades. Previous 



