424 



THE AMERICAN NATURALIST [Vol. LIII 



Brennen hervorruft" (according to v. Wissel, 1898, p. 

 597). 



Stimuli initiated in several different ways may serve to 

 elicit discharge of tlie repugnatorial glands, as : stroking 

 the mantle with a blunt point ; pinching it with forceps ; 

 applying solutions (5/8 M) of NaCl or (less effectively) 

 LiCl, or of methyl or ethyl alcohol (5 M). Touching or 

 pinching the periphery of the mantle itself does not lead 

 to discharge, but on the contrary leads to localized retrac- 

 tive puckering; when a gland is erected, preparatory to 

 discharge, stimulation of that gland causes it to collapse, 

 or ''wilt," a process similar to that following normal dis- 

 charge. If the dorsum be scratched until erection of the 

 glands occurs, and then NaCl solution be applied to one of 

 them, it is found, as also with mild faradization, that two 

 or even three successive discharges are possible ; but the 

 later out-pourings of secretion are very meager as com- 

 pared with the first explosive ejection. About twenty- 

 four hours is required for the regeneration of a new 

 supply of repugnatorial substance. 



Before the glands discbarge, the edge of the mantle 

 curls upward, forming around the Onchidium an encircling 

 saucer-edge bearing the now prominent glands ; thus, de- 

 pending upon the intensity of excitation, the glands come 

 to point more and more dorsal, and in this position release 

 their contents. Not only so, but the individual gland 

 papilliE are themselves further directed in a general way 

 toward the irritated spot, so that if a slip of glass be held 

 horizontally 1 or 2 cm. above an Onchidium the back of 

 which is at one point subjected to mild faradic excitation, 

 the contents of all the discharging glands are found to 

 impinge upon very nearly the same point ; sometimes all 

 the discharges converge to an area of less than 3x3 mm., 

 immediately above the spot irritated. The gland or 

 glands nearest the site of stimulation are the first dis- 

 charged, and the implication of more distant ones depends 

 on the degree of stinnilntion. 



Semper (1881, p. :57i' rl ,r,/.) vnu>ldvvvd iliat the dorsal 



