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. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. GEOTROPISM OF THE MARINE SNAIL, LITTORINA LITTOREA. 73 covered above so that the sunlight penetrated parallel to the glass plate and through the open portion, c. So arranged, the intensity and direction of the rays of the sunlight had to affect the reaction of the snails to gravity. Since the animals were negatively heliotropic, it was expected that most of them would crawl downward in this arrangement. Their heads, therefore, were placed upward at beginning, so that definite movements of orientation could be observed. The.

. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. GEOTROPISM OF THE MARINE SNAIL, LITTORINA LITTOREA. 73 covered above so that the sunlight penetrated parallel to the glass plate and through the open portion, c. So arranged, the intensity and direction of the rays of the sunlight had to affect the reaction of the snails to gravity. Since the animals were negatively heliotropic, it was expected that most of them would crawl downward in this arrangement. Their heads, therefore, were placed upward at beginning, so that definite movements of orientation could be observed. The.  Stock Photo
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. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. GEOTROPISM OF THE MARINE SNAIL, LITTORINA LITTOREA. 73 covered above so that the sunlight penetrated parallel to the glass plate and through the open portion, c. So arranged, the intensity and direction of the rays of the sunlight had to affect the reaction of the snails to gravity. Since the animals were negatively heliotropic, it was expected that most of them would crawl downward in this arrangement. Their heads, therefore, were placed upward at beginning, so that definite movements of orientation could be observed. The. FIG. 3. results after one minute were as follows: Of 50 animals in 15 trials, 5 or 10 per cent, had crawled upward, all diagonally; 37 or 74 per cent, had crawled downward, 22 of them being well oriented and 15 diagonally; 8 or 16 per cent, crawled horizontally and consequently across the lines of direction both of light and of the effective component of gravity. The predominance of downward movement was no doubt due to the intensity and direction of the sunlight. This point be- comes clearer in the next experiments, but it is clear that the surface-film has nothing to do with such reactions. Experiment D.—With the same point in mind, other experi- ments were made in a similar way, but the animals were placed about 1.5 cm. above the surface of the sea-water. In this case 29 individuals out of 50 oriented themselves downward, and crawled in that direction through the surface-film of sea-water into it. Three crawled horizontally at the surface-film instead of going into the sea-water. 18 or 36 per cent, crawled upward.. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Marine Biological Laboratory (Woods Hole, Mass. ); Marine Biological Laboratory (Woods Hole, Mass. ). Annual report 1907/08-1952; Lillie, Frank