NATURAI. HISTORY OF AMERICAN LOBSTER. 237 



The swimmerets of the lobster were also proved to be quite sensitive under most 

 conditions, as well as the thoracic sterna, the wings of the seminal receptacle of the 

 female, and even the hard carapace, which was nearly as responsive to weak acids as 

 is the soft skin of the frog, and the scratching movements made by the legs in the direc- 

 tion of the stimulated part are essentially the same in each case. We concluded that 

 the sense organs were the setae, reenforced by sensory buds, which lie in the tissues 

 beneath the hard shell, but open upon it by capillary ducts. For other reasons these 

 perplexing structures were given the name of tegumental glands. We have found no 

 reason to alter this conclusion, and can still point to the upper lip as a supporting case. 

 The labrum while possessing no true setae is highly responsive to chemical stimuli, and is 

 full of the organs in question, which open by ducts all over it in the lobster, but are 

 most abundant on the under concave surfaces, to which a greater sensitiveness was 

 attributed in the crayfish by Lemoine; here the ducts are clustered in large sieve-like 

 plates bearing 60 to 70 holes each. We have further shown (see p. 232) that the labrum 

 is not only well supphed with nerves, but possesses an independent ganglion of itsown. 

 That these labral organs are not glandular in function might be also indicated by the 

 fact that the upper lip is always clean in the lobster, and free from anything suggesting 

 a glandular secretion. 



Experiments on the crayfish by Bell and others have shown conditions essentially 

 similar in most respects. In getting food, sight playjUttle part, the bhnded crab or 

 crayfish going unerringly to the bait. This is certainly true of the lobster, as the 

 experience of fishermen amply proves. Apparently through their chemical sense organs, 

 for we do not seem warranted in using either the word "smeU" or "taste," they become 

 aware of the presence of food, and are attracted to it, whUe in the crayfish accuracy in 

 the localization and in the seizure of the food seems to be secured through the medium 

 of touch. 



Bethe, who performed some strking experiments with the common green crab, 

 Carcinus mcenas, found that the chemical reaction was the most important in its search 

 for food. 



The mouth parts, says Bell, in summarizing Bethe's results, seem to be more sensitive to chemical 

 stimulation than the antennae or the antennules, since the animals react when the latter are removed. 

 The threshold of chemical stimulation is extremely low, for the animals react most vigorously to the 

 trail left in the water by a finger that has been in contact with meat, and greedily devour filter paper 

 which has barely touched meat, but to really clean filter paper they pay no attention. 



Holmes and Homuth ° have repeated Bell's experiments on the crayfish and tested 

 its reactions to chemical stimuli after removal of the antennules and antennae, and 

 after destruction of the brain and a section of the ventral nerve-chain. They confirmed 

 the old opinion that the olfactory sense was lodged chiefly in the outer branches of 

 the antennules, but found it exercised in a lesser degree by the antennae, the mouth 

 parts, great cheKpeds, and the slender legs. Destruction of the brain or nerve cord 

 tended if anything to slow down the reactions, but did not put an end to response. 



"Holmes, S. J., and Homuth, G.S.: The seat of smell in the crayfish. Biological Bulletin, vol. xvm, p. 155-160. Boston, 

 1910. 



