156 S. J, HOLMES AND E. S. HOMUTH. 



give this reaction first. The farther the Carcinus is from the meat 

 the later will begin the reactions. Soon after the animals begin 

 to react they move about and usually in quite a direct line 

 toward the meat. The nearer they approach the food the faster 

 they go. That the eye plays little part is evidenced by the fact 

 that blinded forms go toward the meat with just as much cer- 

 tainty. If a piece of meat is passed over the rocks at the bottom 

 of the aquarium a Carcinus will follow this scent and often pick 

 up every stone, which has been in contact with the meat, and pass it 

 to the mouth, but as soon as the stones come in contact with the 

 maxillipeds they are rejected. 



If the antennules are removed CarcintLS reacts to food but only 

 when it is placed a short distance from the mouth parts. The 

 latter are regarded by Bethe as also sensitive to chemical stimuli. 

 In the amphipod Amphithoe^ one of the present writers found 

 that the antennules were important olfactory organs, but that 

 there remained a certain but much diminished power to detect 

 food at a distance from the mouth parts after the antennules, or 

 even the antennules and the antennae were removed. Other 

 species of amphipods were found to make exploring movements 

 of the antennules when in the presence of food. 



Nagel's experiments with amphipods and isopods failed to 

 elicit any positive response, although some species gave negative 

 responses to disagreeable or irritating substances. The terrestrial 

 isopods, Oniscus, Porcellio and Armadillo he found to be quite 

 insensitive to strong substances like cedar oil and benzol. It is 

 not difficult, however, to obtain very decided reactions from ter- 

 restrial "t- to the vapor of acetic acid and ammonia even 

 after remc ^he antennae. 



Many pa s have appeared dealing with the organs of smell 

 in Crustacea but conclusions regarding their functions have been 

 based more on morphological grounds than on the results of 

 experiment. One of e most recent papers on the chemical 

 sense of Crustacea is i *" of Bell,^ who worked on the reactions 

 of the crayfish. Bel ^r^^lied meat juice by means of a fine- 

 pointed pipette, to various parts of the body. To render it evi- 



1 Biological Bulletin, Vol. 2, p. 165, 1901. 

 ''■Jour. Comp. Netir. and Psych., 16, 299, 1 906. 



