266 SELIG HECHT 
is either excluded by the closing of the entrances to the body, or 
it is thrown out by a discharge of water. I have never observed 
any positive response to a stimulus in this species. This is not 
unexpected from its mode of existence. The animals are entirely 
dependent for their supply of energy on what is brought in by the 
water current, and they merely exercise a choice by rejecting 
anything which acts as a stimulus. 
2. Nervous relations 
Among higher animals, the tunicates are peculiar in the 
concentration of the entire central nervous system into a single 
inter-siphonal ganglion. In Ascidia atra, according to Hilton 
(13),? this is a roughly cylindrical mass, on one side of which is 
to be found a rather unusual neural gland (Metcalf, 00). It 
gives off many more nerve trunks than are usually described for 
this genus of ascidians. From the oral end therg arise three large 
nerves, which go to the region of the oral siphon. Several nerves 
leave the atrial end, while from the middle of the ganglion there 
emerge three large nerves, four smaller ones, and many minute 
ones. It is significant that all the nerves contain both afferent 
and efferent fibers (Hilton, 13, p. 116). 
Practically nothing is known of the nerve endings in ascidians. 
The same may be said of the presence of sense cells. Hilton 
describes the fibers of the oral nerves as ending in the oral tenta- 
cles, but fails to state whether they form free nerve terminations 
or arise from sense cells. Lorleberg (’07), after prolonged in- 
vestigation of the nervous system of Styelopsis, concludes that 
there is a complete lack of sense cells, but that there are un- 
doubted free nerve terminations present. 
In relation to the reactions of ascidians, one point is clear: 
the only demonstrated means of direct nervous communication 
between the siphons is by way of the ganglion. The ganglion, 
however, has more than the mere conducting function supposed 
2 This author refers to the species as Tunica nigra. I have it from Professor 
Mark that Hilton’s work was done on Ascidia atra. Moreover, his description 
of the species as the “ascidian very abundant on Agar’s Island” leaves no doubt 
as to its identity. 
