SENSORY REACTIONS OF CHROMODORIS ZEBRA 297 



ness disd,ppears. Chromodoris will slowly recover after fifteen min- 

 utes' exposure to 4°C. This is probably the lowest temperature which 

 Chromodoris can endure for a similar period and yet recover. 



At temperatures of 32° to 35°, the genital papilla becomes extended, 

 in some cases immediately; after fifteen to thirty minutes the pro- 

 boscis is almost invariably protruded. The gills also contract notice- 

 ably upon first immersing the nudibranch, but are subsequently ex- 

 tended very fully. The attachment of the foot is rarely accomplished, 

 the animal lying upon its side in an apparently 'exhausted' state. 

 Tactile irritability is very low. In a number of instances the rhino- 

 phores could not be caused to retract when the head region was stimu- 

 lated. Chromodoris survives an hour's exposure to sea-water of 32° 

 to 35°. 



Immersion in water at 37° to 38° causes the nudibranch to become 

 active for several minutes, but a quiescent state quickly ensues. Tactile 

 reactivity disappears, except on the gills. Some individuals recover 

 from a thirty-minute exposure to this degree of heat. 



At 40°, the nudibranch showed writhing movements for one minute, 

 and then became quiet and remained more or less contracted. After 

 two minutes the gills plumes were curled, but later became extended, 

 and were then found reactive to touch. The rest of the body surface 

 seemed insensitive to touch. After twenty minutes the tactile response 

 of the gill became very weak. 



At 42°, mild writhing movements were evidenced for two minutes; 

 the gills sometimes became curled, but in any event were quickly 

 expanded. After three to four minutes no tactile responses were ob- 

 tained from the gills. Chromodoris withstands six to ten minutes 

 exposure to this temperature, but does not fullty recover. 



Immersion in water at 44° leads to rather sharp writhing move- 

 ments, lasting several minutes, after which the animal is much elon- 

 gated with the gills expanded. No tactile responses from the gills after 

 three minutes. One individual showed some movement of the foot and 

 body when transferred to sea-water at normal temperature after being 

 for seven minutes at 44°. 



Temperatures above 45° usually produce death, accompanied by 

 considerable contraction, within five to ten minutes. 



There appears from these tests to be something akin to 'cold' 

 activation at about 10°, at which temperature the gill crown is 

 partially contracted; some general body movements are also ex- 

 hibited upon immersing tha animal in sea-water cooled to this 

 degree. The anaesthetising effect of low temperature is very 

 evident in Chromodoris. Noticeable contraction of the gills 

 occurs also at 32°, which represents probably the minimal tem- 

 perature for a distinct 'heat' stimulus. 



