9O CHAS. W. HARGITT. 



Both in experiments and in nature there seems to be no evidence 

 of its operation. Specimens attach themselves to the bottoms 

 of boats, to overhanging rocks, etc., and seem quite indifferent 

 to its influence. We may therefore proceed to consider the main 

 question at issue, namely, that of light. 



Of the 90 specimens having a sub-vertical attitude about (>o 

 were on the bottom of the aquarium, which leaves 30 of this 

 class among those located on the back and end walls. In other 

 words, twice as many of the vertical specimens were located on 

 the bottom as on the sides. But let it be remembered that of the 

 total 150 specimens in the aquarium about 94 were planted on 

 the bottom while only 56 were located on the walls. Further, 

 it is to be noted that those located on the bottom must assume a 

 sufficient degree of elevation to afford a free expansion of the 

 gills; to those on the walls this is not essential. On the other 

 hand, of the 60 specimens which had assumed a horizontal, or 

 downward attitude about 25 were among the bottom specimens, 

 while the other 35 were among those attached to the walls. 

 Expressed in percentages we have the following: Of the whole 

 number about 60 per cent, showed a more or less vertical aspect, 

 while 40 per cent, showed otherwise, i. e., a downward inclination. 

 Of those planted on the bottom about 70 per cent, showed a 

 vertical tendency, and about 30 per cent, were inclined downward. 

 Of those on the walls about 65 per cent, inclined downward, 

 while 35 per cent, inclined toward the vertical. 



Now, how shall one interpret these varying aspects? Accord- 

 ing to theory, " If the rays of light fall vertically from above into 

 the aquarium, Spirographis directs its tube vertically upward, 

 exactly as a stem grows vertically up into the air." In the case 

 before us the light comes vertically from above, yet a large per cent, 

 of the specimens fail to direct the tubes vertically upward. Of 

 wall specimens 65 per cent, incline downward, or are horizontal 

 in relation to light. Of those on the bottom the per cent, curving 

 downward is much smaller, but still too great to be explained 

 as merely incidental, or by the naive suggestion "Here, however, 

 where free-swimming forms easily disturb the orientation <>t 

 Spirographis, it is not so perfect as when all possible- disturbing 

 causes are avoided, as in an aquarium used only for such experi- 



