12 Papers from the Marine Biological Laboratory at Tortugas. 



Several experiments were devised to determine if Ocypoda would react 

 to odors, and although the results were not conclusive they were of some 

 interest. 



Experiment i. — Pieces of coral and small fish (Atherina) were dropped 

 alternately near a crab. They ran for each and often carried the coral as 

 well as the fish away with them. Precaution was not taken, however, to 

 have the pieces of coral free from the odor of fish. 



Experiment 2. — Atherinas soaked in carbon disulphide were thrown to 

 the crabs and these w^ere at once seized in all cases and carried into the bur- 

 rows. As far as could be observed this ill-smelling liquid had no effect on 

 the ocypodas. 



Experiment j. — Poured aqua ammonia down a burrow containing a crab. 

 This burrow had two openings and a strong odor of ammonia came up 

 through the second opening, showing that it penetrated through the entire 

 burrow. This did not cause the crab to come out of its burrow until lo 

 minutes at least had passed, when it came out unaffected, as far as could 

 be observed. 



Experiment 4. — An atherina was wrapped in several thicknesses of news- 

 paper, the ends being left open and care taken not to get fish juice on the 

 newspaper. (The paper extended an inch beyond the fish at both ends.) 

 This was then wrapped in Swiss book, tied at the middle, and dropped near 

 the opening of a burrow. The crab soon came out, pinched it, and attempted 

 to bite it at the open end. It seemed to react as it would toward an uncon- 

 cealed fish, and it is not probable that the juices of the fish came in contact 

 with the mouth-parts. Finally the package was taken down into the burrow, 

 which was then closed up. 



The same experiment was repeated, substituting a roll of newspaper for 

 the fish and wrapping with Swiss book as in the former case. This package 

 was then dropped and was almost at once grabbed and pinched, but soon left 

 as though there were nothing attractive about it. 



Experiment 5. — In this experiment a bowl-like hole was dug and athe- 

 rinas were put in the bottom of it. They were then covered over with a 

 layer of sand about an inch thick, so that they could not be seen, but so that 

 the odor could be detected by the experimenter. A screen made of y^-'mz\\- 

 mesh wire was then put over the excavation, so that the crabs could not 

 reach the fish without digging under. Great care was taken not to allow 

 the juices of the fish to get on the screen or the sand surrounding it. At the 

 expiration of 10 hours the ocypodas had not made an attempt to dig down 

 to the fish. There were many tracks on the sand, however, showing that 

 the crabs had been examining the region. A crab was observed crawling 

 over the screen, pinching the wires of the same and then rubbing its chela 

 over the mouth-parts, which behavior is typical of the feeding reaction. 

 This was repeated by the same crab, and seems to afford strong indications 

 that Ocypoda may react to food at a distance through some other sense than 

 those of sight or contact (figs. 4 and 5). 



Experiment 6. — A young ocypoda which had not been fed for a day was 

 used in this experiment. The eyes were painted with a mixture of shellac 

 and lampblack, so that they did not react to shadows or to the movements 

 of the hand near it. A fresh atherina was held within about 2 or 3 mm. from 

 the mouth-parts for about 3 minutes. So far as could be seen the crab did 



