68 < II VS. \V. HANI-TIT. 



merits in every practicable way, and under a range of conditions 

 which would eliminate as fully as might IK errors of inference 

 based on limited experiments or fauhy en\ ironnu nt.il conditions. 

 Details on these points will be given in later section;, of the paper. 



PROTULA PROTULA. 



This annelid is a very familiar element of the fauna of the 

 Bay of Naples. Its large size, often 175 mm. in length by ,s s 

 mm. in diameter, its fantastically coiled tube, and the brilliant 

 orange-red gills which are splendidly displayed during expansion 

 conspire to make it a conspicuous object. The sensitiveness of 

 the creature to differences of light intensity, such as that involved 

 in the intervention of shadows, was one of the first aspects of 

 behavior to engage my interest many years ago, some brief 

 notice of which was made in my early paper ('06, pp. 311, 314). 

 These observations I have verified again and again during tin- 

 present series of experiments. Careful comparisons of many 

 specimens in their reactions reveal the fact of marked individual- 

 ity as expressed in the variability of behavior shown from day 

 to day. It is not necessary to go into details concerning this 

 point. What has been pointed out in the case of Ilydroidcs 

 dianthus ('09) is confirmed in the case of Protula. Certain speci- 

 mens were especially sensitive and extremely active in response, 

 while others would show the very opposite; and it was not un- 

 usual to find specimens which seemed totally indifferent to 

 shadow stimuli. Again, specimens might prove quite sensitise 

 at a given time and very indifferent at another. But let it be 

 noted that some specimens seemed normally to be highly sensi- 

 tive, while others seemed normally quite tin- opposite. Again, 

 the retraction aspects of behavior, that is, the time a gixen 

 specimen remained in the tube after a given contraction, \\.is 

 remarkably variable. In some cases the emergence was rela- 

 tively prompt, while in others it was extremely slow. In this 

 matter Prolnla differs materially from Ilydroidcs, whose retrac- 

 tion periods are usually and normally very briel. Protnla ohen 

 remained retracted for indefinite periods, otten tor one or t\\o 

 hours at a time, in marked contrast to Hydroides. 



Tubular Aspects. The behavior of Protula as e\]>iv ed in the 



