212 W. J. CROZIER 



observation, however, certain characteristic types of reaction 

 may be made out. 



If the animals are handled with care during collection and 

 subsequently, they may be kept in a healthy condition for some 

 time. Certain preliminary trials with specimens obtained in the 

 summer time led me to state (Crozier '15) that Ptychodera was 

 sensitive to sudden changes of light intensity, but that it was not 

 phototropic. 2 Subsequent work with aninals in better condi- 

 tion, and particularly with numerous individuals collected dur- 

 ing the cooler winter period, has shown this statement to be 

 incomplete. Ptychodera is, in fact, definitely phototropic when 

 the animal is in physiologically good condition. 



No observations seem previously to have been made with 

 reference to the sensitivity of Balanoglossus toward light . Con- 

 sidering their habits in natural circumstances, one would be led 

 to suppose that these enteropneusts would tend to move away 

 from a source of light, or that they would retract as the result of 

 suddenly increased illumination. Assheton ('08) states that the 

 Dolichoglossus studied by him protruded its long proboscis 

 from the mud only at night. The Ptychoderas studied by me 

 are found in sands of rather well defined types, either just below 

 the surface of the sand or between this surface and the under side 

 of flat stones. When uncovered, they promptly burrow again, 

 or, if merely the proboscis and collar have been exposed, draw 

 back into the sand. 



A series of tests was made in which the animals were placed 

 in an oblong aquarium jar and illuminated from one side. The 

 vessel was in a dark-chamber In the first trials the aquarium 

 contained clean sea-water without any sand. The animals were 

 selected from freshly collected stock living in large glass dishes 

 provided with a good supply of their native sand. . I soon found 

 that the Ptychoderas could move about much better if some 

 sand was also placed in the experimental aquarium. 



After being in the dark-chamber for some time before light 

 was admitted, sunlight reflected from a mirror was allowed to 



2 In the hands of the ingenious type setter, this word has, in the note cited, 

 become transformed into 'photographic' 



