THE SENSORY RESPONSES OF CHITON 247 



parts, although 1 M sucrose in rain-water did not, except from 

 the ctenidia. This total concentration (< 6/8 M) is well within 

 the ^osmotic limit,' and indicates that sucrose may be mildly 

 efficient in stimulation. The behavior of maltose also shows 

 faint indications (at 1 M in rain-water) of some stimulating 

 capacity. According to Brooks ('16), sucrose penetrates (plant) 

 protoplasm quite readily, and affects permeability after the 

 manner of a monovalent kation, although not with special ra- 

 pidity. The fact that in Holothuria (Crozier, '15 b) no evi- 

 dence was obtained that sucrose could stimulate the integument 

 — although maltose and glycerin apparently did, while in the 

 experiments of Olmsted ('17 b) and of Hecht ('18) no sucrose 

 effect was detected apart from that exerted through the osmotic 

 pressure of its solutions — shows that some such factor as the 



"3X:^ 



Fig. 14 Showing the manner in which the proboscis is kept in contact with 

 the substratum during creeping. Anterior end, seen from the side: a, proboscis 

 margin ('palp');/3, foot; y, girdle. Arrow shows. direction of creeping. 



time of exposure to the sugar solution (or the concentration of 

 accompanying salts?) may be important in determining whether 

 or not activation occurs. Sensitivity to sugars, even if present, 

 is however, undoubtedly very low on the general soft surface of 

 chiton. With Chromodoris zebra we have found no stimulation 

 induced by maltose or sucrose 1 M in rain-water, applied to 

 various parts of the animal's surface in small volumes from a 

 pipette, the animal being in sea-water. Similar tests with 

 Balanoglossus (Crozier — unpublished experiments) resulted in no 

 detection of activation by 1 M solutions of sucrose or of maltose, 

 c. Independently of their osmotic sensitivity, the soft surfaces 

 of Chiton are also open to activation by dissolved electrolytes, 

 which are much more powerful as excitants than are non-elec- 



