132 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



and touch % Lemoine, who experimented with the crayfish, found that even the thickest 

 parts of the carapace were sensitive, and that the parts which abounded in hairs were 

 the most sensitive. Touching the hairs determined the movement of the claws and 

 thoracic legs. 



Milne Edwards considered the buccal cavity as the seat of the sense of taste, but 

 although the experiments made by Audouin and himself convinced him that the sense 

 was developed, he failed to find any special organs. (55, i, pp. 112-113.) 



Lemoine experimented upon the buccal cavity, and especially the labrum, using 

 a great variety of stimulants, such as salt, pepper, tobacco, ammonia, and electricity. 

 He describes the labrum of the lobster, but, strange to say, did not discover the organs, 

 with which it is packed full. He found that the inner face of this body was extremely 

 sensitive. A nerve enters the labrum on each side. This gives off lateral twigs near 

 the point of entry and numerous terminal branches toward the median plane. He 

 supposed that these terminal filaments supplied the short hairs which were erroneously 

 supposed to cover the surface. 



The setse of Crustacea have tactile, auditory, and probably olfactory functions. 

 The sensory seta is hollow and stands over a canal, which penetrates the integument, 

 and a nerve fiber passes up into the lower part of the canal. (84.) 



The organs of taste in insects, according to Lubbock, are modified hairs, situated 

 either in the mouth or on the organs immediately surrounding it. Nine different 

 antennal organs have been described in the Hymenoptera. Some of these antennal 

 hairs serve as organs of touch and smell, and possibly for hearing also. 



I have already called attention to the fact that while the pleopods are studded 

 with thousands of microscopic glands, these appendages in the male are almost devoid 

 of them. Their occurrence in the brachyura, where indeed they were first described 

 by Braun (23), might support the theory that they had, in such cases, a function to 

 perform independent of the production of cement, since it has been shown that the 

 crabs possess a special cement-forming organ in the epithelial lining of the glandular 

 receptaculum seminis. We must therefore conclude that in the brachyura the work 

 of the glandular receptaculum seminis is supplemented by that of the pleopodal 

 glands, or that the latter possess another function. 



On the other hand, Leydig (122) has maintained that there is a close relation 

 between gland cells and sensory cells, the two kinds of cells resembling each other in 

 general structure and in the disposition of the cell contents. He found in the sensory 

 cells of the skin of some vertebrates what seemed to correspond to cuticular secre- 

 tions in gland cells. 1 



The gland of the type which we have been considering is undoubtedly a very 

 primitive organ in Arthropods. It has probably been modified to perform different 

 functions, with a minimal change of gross anatomical structure. What the function in 

 every case is we can not for the present say with any degree of certainty. While the 

 question is a puzzling one, it seems to me safer to regard all such structures, wherever 

 they occur, in oesophagus, the intestine, the labrum, pleopods, or outer integument of 

 the body, whether in Decapods, Limulus, or in other forms, where they will doubtless 

 be discovered, primarily as glands. We may add that in the labrum, and perhaps in 

 other parts of the external integument of the lobster, and in Limulus, they may have 



1 Jickeli, according to Leydig, believes that in certain Hydropolyps which he studied sensory 

 cells are converted into gland cells. {122.) 



