PHYSIOLOGY OF ASCIDIA ATRA LESUEUR 279 
Ascidia is sensitive to very intense light, it can hardly be called 
photosensitive in the ordinary use of the term. Moreover, like 
the anterior pigment spot of Amphioxus—the ‘eye-spot,’ which 
Parker (’08) has shown to be insensitive to light—the inter-lobal 
pigment spots of Ascidia—the so-called ‘ocelli’—are also not 
photoreceptors. 
IV. TEMPERATURE 
1. Thermosensitivity 
The reactions to temperature changes are practically an un- 
known factor in the physiology of ascidians. The effect of dif- 
ferent temperatures on the reactions of Ciona, which Jordan (’07) 
has investigated, is a matter entirely different from the reactions 
produced by the sudden exposure of the body to different tem- 
peratures. The latter effects were studied by Kinoshita (’10) 
on Ciona on the assumption that the siphon rims were thermo- 
sensitive. : 
In Ascidia the siphon rims are not sensitive to heat. As has 
been described, direct sunlight concentrated on the outside and 
inside of the rims failed to produce any response. Such a beam 
of ight when focussed on a piece of paper caused it to burn in 
very short order; when directed on the bulb of a thermometer 
in the position of the animal, it made the mercury thread fairly 
leap upward. The animals, however, failed to respond. There- 
fore, if Ascidia is sensitive to temperature changes, the irritability 
is not resident in the siphon rims. 
When Ascidia is picked up carefully, it merely closes its siphons. 
If it is at once replaced into seawater, the time required for the 
siphons to open’ again is practically constant for each individual. 
The record of animal VII.18.1 will serve as an example. It was 
picked out of the water and replaced, and the time required for 
opening was taken with a stop watch. The number of seconds 
for four trials are given in table 1. 
Assuming that the animal is thermosensitive, and that the 
sense organs are located on the test, we might expect that trans- 
ferring the animal into seawater at a higher or a lower tempera- 
