NERVOUS SYSTEM OF THE TUNICATE 309 



My interest was first aroused in the subject of tunicate re- 

 actions during a zoological expedition from Harvard University 

 to the Bermudas in 1910, and it led to later investigations carried 

 out in 1913 at Naples. For the opportunity of enjoying the 

 facilities of the Naples Station I am indebted, on the one hand, 

 to Harvard University for a traveling fellowship, and on the 

 other, to the Smithsonian Institution for the use of its research 

 table there. I wish here to express my thanks to the various 

 members of the Naples staff for their services and many kind- 

 nesses during my sojourn. 



In how far Ascidia atra differs from Ascidia men tula in the finer 

 details I cannot say, but in the gross anatomy they are very 

 similar, although in color the former is bluish black and the 

 latter a milky white. Both are from 4 to G inches in length, 

 have a smooth outer tunic unornamented with protuberances, 

 hairs, or other local modifications. The margins of incurrent 

 and excurrent siphons of both species are lobed. The only 

 record of the number of lobes which I have for Ascidia atra is a 

 general statement that the number on the incurrent siphon 

 ranges from 7 to 11, while that for the excurrent is 5 to 6. 

 Hecht ('18) says 8 on the oral and 6 on the atrial. For Ascidia 

 mentula the average number for the former is 9 and for the 

 latter 6. The interlobular margins of both siphons of Ascidia 

 mentula are edged with red pigment, while the lobes themselves 

 • are, as a rule, uncolored. Just proximal to these red edges are 

 situated isolated pigment spots; a single one usually between 

 each lobe on the oral siphon, and two or more in a cluster be- 

 tween each lobe on the aboral siphon. Occasionally an animal 

 was brought to the laboratory which was totally brick red. 

 Ascidia atra, on the other hand, is a velvety bluish black all 

 over, due to the presence of pigment in the outer tunic. I never 

 ran across one, however, where pigment was restricted to only 

 the margins of the siphons. Ascidia mammillata, like Ascidia 

 mentula, is whitish except for the pigment spots, in this case 

 black, around the incurrent and excurrent apertures. Ciona 

 intestinahs has red pigment spots on the margins of the siphons. 

 Mention is made of these details of pigmentation because they 



