224 



HELEN WOODBRIDGE. 



determined. The results of six such experiments including 

 the four previously reported are indicated in the following table. 



TABLE SHOWING THE RESULTS OF Six EXPERIMENTS DESIGNED TO DETERMINE 

 WHETHER OF NOT THE LARV.E " SELECT " EEL GRASS AS A PLACE 



FOR METAMORPHOSIS. 



Per Cent, of Metamor- Per Cent, of Total 



phosing Zooids Attached Area Offered by the 



Experiment. to Eel Grass. Eel Grass. 



1 55-8 ii. I 



2 48.1 18.3 



3 55-2 20.0 



4 43-7 19-4 



5 12.0 14.4 



6 32.8 17.6 



Average 41.23 16.8 



These results indicate that the larvae under these laboratory 

 conditions, tend to " select " eel grass as a place for permanent 

 attachment and metamorphosis. It seems safe to assume that 

 the responses of the larva which tend to bring it into contact with 

 eel grass under the conditions in the experiment, would function 

 in a similar way in the natural habitat of the larva. Granted, 

 then, that a certain amount of " selection " does take place in 

 determining the place of metamorphosis, what are the specific 

 responses of the larvae and what the stimuli bringing about 

 these responses whereby the larva is led to a place suitable for 

 metamorphosis? Does the eel grass offer any chemical attraction 

 for the larvae ? Does the larva show a positive response to gravity 

 during the latter part of its free-swimming period, thus in its 

 natural habitat coming in contact with the lower parts of the 

 eel grass blades? Is the negative response to light responsible for 

 this " selection " ? Does the larva tend to follow surfaces, thus 

 keeping it in a favorable locality once it has reached it? Does 

 the response of the larva in swimming upward when renewing 

 activity play any part in determining its place of attachment and 

 metamorphosis? These are some of the questions which sug- 

 gested themselves. Enough of them have been answered to sug- 

 gest at least which factors function in determining the place of 

 metamorphosis of the larvae. 



Chemical Attraction. In considering the question of the " selec- 

 tion " of the eel grass by the larvae, it seemed at first quite pos- 



