86 ('HAS. \V. II \Ki,iTT. 



behavior of the- specimens in thi>, \vhile differing in various 

 details, have shown a striking similarity to that of specimens in 

 the former, as well as that of the first series in the large aquaria. 

 As remarked in the outset, the entire series of experiment-- have 

 involved no appreciable deterioration of the health or vigor of 

 the specimens. As an evidence of this may be mentioned tin- 

 fact that one very young specimen among those used in tin- 

 control tank showed an apparently continuous growth, haxing 

 nearly doubled its original size. The growth in this case seems 

 to have been real and normal, and not apparent as was the case 

 with Hydroides, mentioned in a previous section. 



Third Series. Early in March it was found desirable to change 

 rooms in the laboratory, and I came into possession of one 

 admirably adapted to light experiments. Advantage was taken 

 of this circumstance to continue the experiments with Spiro- 

 graphis under light conditions which were exceptionally good. 

 In the room were two large aquaria, one of which I devoted 

 exclusively to this experiment. The aquarium was arranged with 

 its side facing the window and at a distance of about two meter-. 

 By covering the back, ends and top of the aquarium \\ith a 

 black opaque screen, and with windows also provided with ad- 

 justable shades, one was able to directly control the light condi- 

 tions at will, as to source, directness and intensity. The experi- 

 ment was begun with eight specimens, all of which \\en- placed 

 with heads facing away from the light, and two other- suspended 

 head down by attaching them to sides of the o\ erllow pipe, as 

 in the similar experiment in series I. Other specimens were 

 added a few days later making a total of twenty comprising the 

 experiments. As before some two to four days were required 

 for specimens to become attached to the aquarium. In tin- 

 present case to insure prompt and precise location several were 

 secured to a given place by putting over the terminal base o| 

 the tubes a small weight, such as a shell or rock fragment. 

 As before the first indication of reaction was the usual upward 

 curve of the oral end of the tubes, enabling the creature to I reel \ 

 expand the gills. This reaction has little, it any, relation to 

 orientation movements, as it occurs usually in all cases and under 

 almost all conditions, whether in light or darkness. 



