SELIG HECHT 149 



1896). If the intensity of the stimulus is great, this may be accom- 

 panied by a shortening of the animal on its long axis. This retraction 

 reflex has already become familiar due to the work of Loeb (1902) 

 and of Jordan (1908) among others (see Hecht, 1918, b) especially in 

 its relation to the removal of the ganghon of Ciona. 



It is the response of Ciona by means of the retracting reflex that 

 forms the basis of the experiments which follow. 



3. The orange or red pigment spots on the rims of the siphons are 

 a prominent characteristic of ascidians. Ciona possesses eight on the 

 oral rim and six on the atrial. These pigmented masses have been 

 called ocelli on the assumption that they are the photoreceptors of 

 Ciona. 



Experiments designed to ascertain the location of the photic sense 

 organs showed that the anterior pigment spots were not sensitive to 

 light. A beam of light focussed upon them failed to produce the 

 characteristic reaction. Moreover, their complete removal in no 

 way interfered with the sensitivity of the animal. The protocol of 

 Animal 25.1 gives the details of such an experiment. 



Animal 25.1. 

 Time. 



11 .00 In dark room. 



2 .25 Exposed to light, 120 candle power, reaction time 3.5 sec. 



2.35 " " " 120 " " " " 2,.2i " 



2.44 " " " 120 " " " " 3.2, " 



2.50 Dirty translucent test of animal removed. 



4 . 30 Exposed to light, reaction time 1 . 7 sec. 



4.37 " " " " " 1.4 " 



4.44 " " " " " 2.2 " 



4.50 Rims cut away to remove the ocelli of both siphons. 



7 .41 Exposed to light, reaction time 1.4 sec. 



7.49 " " " " " 1.6 " 



8.00 " " " " " 2.0 " 



10.00 " " " " " 1.9 " 



Of fourteen animals operated in this way, two were killed acci- 

 dentally. The remaining twelve all gave the same results as the one 

 presented in detail. It is clear, therefore, that these pigment spots 

 are not photoreceptive organs (cf. Hecht, 1918, h). 



It has already been shown that although the general body surface 

 is sensitive to hght, the resulting activity is a purely local one. Gen- 



