ACTIVITIES OF THE AMAROUCIUM TADPOLE 253 



the presence of directive rays of light, but the fact that 43 per 

 cent of the tadpoles in experiment 12, in which light was absent, 

 became attached to the bottom, shows that the positive geo- 

 tropic response is not entirely conditioned by the presence of 

 light. 



That the behavior of tadpoles in their normal habitat is prob- 

 ably not very different from that observed under laboratory 

 conditions may be inferred from the vertical distribution of the 

 species. 



Amaroucium colonies are found in abundance on the piles 

 of the Vineyard Haven wharf. They are most thickly set in a 

 zone around each pile about 1 foot in width situated just below 

 extreme low-water mark, then, for a depth of about 7 feet, 

 colonies are scattered rather abundantly, but are seldom found 

 on the parts of piles located more than 8 feet below low-water 

 mark. The in-shore piles, standing in water having a depth of 

 8 feet or less, are set with colonies from low-water mark to bot- 

 tom in the same way as the upper 8 feet of piles standing in 

 deeper water. The reason for the absence of colonies from the 

 lower parts of the deep water piles is not evident for, as Van 

 Name"^ and Sumner^ have recorded, the species is common at 

 depths varying from 1 to 15 fathoms on the rocky, gravelly and 

 sandy bottoms of Vineyard Sound and Buzzards Bay, and 

 Sumner, in comparing the distribution of A. pellucidum con- 

 stellatum and A. stellatum, on the basis of eighty-five dredging 

 stations, states of the former that it "was recorded fifteen times 

 from depths less than 5 fathoms, while in over 60 per cent of the 

 cases it was taken at depths under 10 fathoms." 



ATTACHMENT 



Three adhesive papillae, by means of which the initial attach- 

 ment of the Amaroucium tadpole is effected at the close of the 

 free-swimming period, are situated at the anterior end of the 

 body in the median sagittal plane, fig. 1 . Each papiUa terminates 

 at the surface of the tunic in a cup-shaped enlargement which 

 contains a droplet of viscid substance. Toward the close of the 



