NATURAL 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 setse 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 supplied 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 plays little part, the blinded 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 “smell” or “taste,” they become 
aware of the presence of food, and are attracted to it, while 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 antennre 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 a 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 chelipeds, 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. 
a Holmes, * 5 . J., and Homuth, E. S.: The seat of smell in the crayfish. Biological Bulletin, vol. xvm, p. 155-160. Boston, 
1910. 
