THE AMERICAN LOBSTER. 
133 
a secondary sensory function. I have not examined tlie glands which occur in the 
alimentary tract, and can not say whether they possess a precisely similar structure. 
Upon the supposition that the tegumentary organs are never sensory in functiou, 
we would have to conclude that the reactions which were obtained upon stimulating 
the dead shell had their seat in sensory elements in the vicinity of hair pores, and that 
the sensory hairs themselves are open at the tip, or at least have thin walls. I have 
usually found sensitive areas covered with setae, 1 and while these do not normally 
open at the tip, the cuticle is so thin at this point that chemical stimuli might be readily 
conducted through them. 
There is, however, one organ which is very sensitive to chemical sti muli, and 
which is entirely devoid of true setae in the adult animal. This is the labrum or upper 
lip. Its structure certainly favors the view that the peculiar tegumental organs which 
it contains in such abundance may be the seat of the sense of taste. 
There can be no doubt that the labrum is very sensitive to various stimuli, as 
Lemoiue clearly showed many years ago. In the specimens which I examined with 
particular care no set® of the ordinary kind were present on either the upper or lower 
sides, and the only direct channel for the passage of chemical stimuli from the surface 
of the dead cuticle to sensitive structures below it were the ducts of the tegumental 
glands. After the labrum had been cleaned by boiling it in a strong solution of potas- 
sium hydrate, the cuticular structures were clearly demonstrated. The only setae 
present lie in four small rounded clusters of 12 to 15 each, near the base of the labrum 
and on its upper surface, where the cuticle has been reenforced by deposits of lime. 
These setae are microscopic, measuring only one-tenth millimeter in length. Moreover, 
each is traversed by a duct which apparently opens at the surface and without doubt 
belongs to a tegumental gland. The upper surface of the labrum is abundantly 
sprinkled in other places, especially about the tip, with the minute pores of glauds. 
These are sometimes in clusters, and their aggregate number is very great. When we 
examine the inner surface of the labrum we see it covered with sieve-like patches, each 
sieve containing sometimes as many as 60 or 70 holes, the openings of tegumental 
glands. At the anterior end these merge together so that the openings are exceed- 
ingly numerous. (Compare figure by Lemoiue, 118.) 
Lemoine evidently mistook the ducts in the sieve-like areas for hairs, and has 
figured them incorrectly. The ducts project from the inner surface of the cuticle, 
(compare fig. 170) and in no instance were true setae or hairs present on any part of the 
adult labrum. 
Experimental evidence seems thus to point to the possession of a subsidiary gus- 
tatory function on the part of tegumental organs of the labrum, and possibly of other 
appendages about the mouth. This would imply that the stimulating particles are 
conveyed to the lumen of the organ, and thence to the central rosette. It would 
of course be absurd to suppose that the apparently similar organs in many other 
parts of the body, as in the carapace, possessed a similar function. While such a 
conclusion is not perfectly satisfactory, it is at least worthy of consideration. 
1 The walls of the seminal receptacle contain very few glands, hut are copiously supplied with 
clusters of setae. As I have already shown, they are very sensitive to chemical stimuli. 
