238 ELECTRO-PHYSIOLOGY CHAP. 



conditions in the intestine, more particularly in the colon of 

 Herbivora. This, however, obviously makes any exact investiga- 

 tion of the local changes arising at the point of contact itself as 

 good as impossible. With kathodic stimulation, on the contrary, 

 they are very apparent, inasmuch as a small, but sharply-de- 

 fined, transverse swelling is formed, with only minimal total 

 shortening at the point where the current leaves the muscle. 



The smooth masticatory muscles of Echinus esculentus exhibit 

 a no less remarkable and characteristic response to electrical 

 excitation with the galvanic current, the reactions, moreover, 

 being much more rapid than in Holothurian muscle (29). The 

 calcareous skeleton of the so-called lantern of Aristotle consists 

 of five symmetrical segments, each again consisting of several 

 pieces. The segments are joined together partly by bands, 

 partly by very strong muscles, which are partially very 

 regular in structure. This is in particular the case with the 

 five very short, but quite parallel-fibred muscles, which at the 

 inner basal surface of the lantern connect the five, long, movable 

 chalk ribs, that run out radially from the central cesophageal 

 cavity towards the periphery, where they curve down over the 

 lateral surfaces of the lantern. Besides these five muscles, 

 which form a closed ring, and are each, in large specimens, l'.~> 

 cm. long, and about 4 mm. broad, the other larger muscles, 

 which are inserted into the jaws, and move the teeth set into 

 them, and also fill up the intermediate space between, are very 

 convenient for experimental purposes. No especial preparation 

 is necessary for the first orientation experiment. It is sufficient 

 to divide the sea-urchin with scissors into an upper and lower 

 half, breaking away as much of the shell from the oval part 

 containing the lantern as will give convenient admission to the 

 electrodes. After drawing the teeth with forceps, the membranes 

 that partly cover and partly connect the muscles must also be 

 removed, and the preparation is then sufficiently ready i'nr 

 experiment. If it is now dipped in a vessel of sea-water, which 

 is as indifferent for these muscles as for those of Holothuria, so 

 that only the base of the chalk pyramid with the ring of muscle 

 projects freely, and any point along any one of the five muscles 

 is brought into unipolar contact with the fine-pointed kathode, 

 while the other unpolarisable electrode dips into the water of the 

 vessel, the formation of an idio-nmscular swelling will be even 



