130 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



placed on the intersterual membranes of the abdomen, but if laid upon either the inner 

 sides of the pleura or upon the surfaces of the pleopods the reaction is more marked 



If clam juice is placed on the mouth parts, as upon the flattened basal segments 

 of the second maxilla? or first pair of maxillipeds, vigorous chewing movements are 

 immediately begun, and are continued for several minutes. If the stimulus is applied 

 to one side, the movements are at first restricted to that side only, but eventually, in 

 some cases, the appendages of the opposite side begin to move also. 



If clam juice is dropped upon the swimmerets of the female, a response is usually 

 forthcoming, and the same is true if this stimulus be applied to the terminal segments 

 of the walking legs. In the case of the large chela? the response may be very slight. 

 In one instance, where three females and one male were experimented upon, the 

 abdominal appendages gave no response to clam juice, but the mouth parts were 

 always extremely sensitive. In this case the pleopods gave a marked reaction when 

 touched with weak acetic acid. 



As a rule, the pleopods of the female were more sensitive to the various stimuli 

 than those of the male. The abdominal appendages of the body give no reaction 

 when breathed upon, and show but slight sensitiveness to heat. Weak electrical 

 currents from an induction coil produce marked responses in the maxilla? and first 

 pair of maxillipeds, and if the swimmerets are touched by the electrodes, violent 

 contractions of the flexor muscles of the abdomen speedily follow. 



The preceding experiments would lead us to suppose either that certain areas of 

 the skin of the body and appendages are very sensitive to a variety of stimuli or 

 that the skin or parts below it possess special sense-organs. In either case, excepting 

 electrical stimuli, the organs must be reached by means of the canals which penetrate 

 the inert cuticle. 



Since there are only two possible roads for the entrance of chemical stimuli — the 

 hair pores and the pores of the glandular ducts — the question is therefore raised 

 whether the glands possess a subsidiary sensory function. If it could be shown that 

 the seta? of the carapace were not perforated at their tips, it would be certain that 

 ammonia vapor could not enter them 1 and extremely probable that the reaction from 

 this chemical stimulus had its seat in the gland. I believe that these organs do 

 possess such a subsidiary function, and that this is shown to be the case by a study of 

 the sensitive labrum, in which hair pores and their corresponding seta? are entirely 

 absent. 



The function of the tegumental glands in various parts of the body has been a 

 subject of much embarrassment. Max Braun (22) thought that the oesophageal glands 

 of the crayfish were salivary organs. Vitzou inclines to acquiesce in this opinion, 

 but admits that the presence of organs of exactly the same structure in the walls of 

 the intestine (in Palinurus) is puzzling, to say the least. 



Professor Patten (150) has recently discovered certain organs in Limulus to which 

 he attributes a sensory function. They have essentially the same structure as the 

 tegumental glands of the decapod Crustacea. There occurs in front of the mouth of 

 Limulus, on the middle line, a wart-like swelling, which Patten regards as the cuticular 

 portion of an olfactory organ. "Directly beneath the ectoderm", he says, there "are 

 a great many — at a rough estimate, from 1,500 to 2,000 — clear, flask-shaped sense buds, 

 each of which is connected by a narrow neck with a cuticular canal." The structure 



1 Where the set,B are moist it might be possible for ammonium vapor or any other chemical 

 stimulus to reach the sensory cells by diffusion through the thin chitinous wall of the tubular hair. 



