NERVOUS SYSTEM OF THE TUNICATE 327 



There was a certain circularity in the movement of the local 

 contractions around the oral rim, especially seen in diagrams 15 

 to 20, where the invaginated part occupies successively pro- 

 gressive positions around the margin. These single local con- 

 tractions seemed to summate in effect and to produce, after 

 the completion of two or three, a more general reaction of the 

 whole margin as in nos. 4, 6, 10, 21, 24. 



REACTIONS OF TUNICATES TO LIGHT 



From a consideration of the distribution of pigment one might 

 well be skeptical of the photoreceptive nature of these pigmented 

 regions. As a rule, in Ascidia mentula the pigment is restricted 

 to a narrow interlobular band at the rim and to one or two 

 subjacent spots, but often it is more or less extensively dis- 

 tributed over the siphons, sometimes coloring even the whole 

 body surface. Another genus, Cynthia papillosa, is character- 

 istically red all over, and Ascidia atra is entirely black; in Ciona 

 intestinalis, again, the spots are red, while in Ascidia mammillata 

 they are black, and in both they are localized on the margins of 

 the siphons. From this diverse distribution and color of the 

 pigment, therefore, one would hardly expect it to be associated 

 with any photic sensitivity of the animal. Ascidia mentula, 

 Ciona and Ascidia atra were tested at Naples while Ascidia atra 

 had previously been tested at Bermuda. 



The surface of the animal's body was explored with a pencil of 

 sunlight. For the results on Ascidia atra, see page 323. The 

 three following tables give the results for Ascidia mentula and 

 Ciona; in tables 1 and 2 the diameter of the beam employed was 

 15 mm. while in table 3 it was cut down to 5 mm. The method 

 of illuminating the animal was to reflect the beam of sunlight 

 with a plane mirror through a cardboard diaphragm of the 

 specified aperture upon the animal as it lay in a depth of 4 to 5 

 cm. of sea-water. Four regions of the body were tested in turn 

 in this manner — incurrent siphon, ganglionic region, excurrent 

 siphon, and the main part of the body. Contraction of the 

 siphons was taken as indicator for the response. If no response 



