NEEVOUS SYSTEM OF THE TUNICATE 315 



That the nerve ganghon is quite dispensable to the response 

 of the siphons to stimulation is evident from the foregoing re- 

 sults. Amputating the siphons, however, involved cutting off 

 the blood-supply from the severed part, and the effect of break- 

 ing all connections with the ganglion was so complicated with 

 interrupting the circulation that no safe conclusions could be 

 drawn with regard to the nervous control exerted by the gang- 

 lion. By removing the ganglion, therefore, without at the same 

 time injuring the circulation, its relation to the siphonal responses 

 could be separately determined. 



C. Extirpation of the ganglion 



Four Ascidiae mentulae were operated upon by excising the 

 ganglia, and they lived long enough for the ganglia to regenerate 

 — a period of about one month. 



Immediately following the operation on two of the animals, 

 the oral siphons began to open, but their irritability to stimulation 

 was greatly reduced. Since the operation was performed with- 

 out the use of a narcotic, this diminution of sensitiveness was 

 probably due to shock. With the lapse of a few days irritability 

 gradually increased, but it never attained the level of the normal 

 animal until towards the end of the month when the nervous 

 tissue had regenerated. Thus, although the ascidians responded 

 to penciling and to tapping on the jar in which they lay, a 

 greater strength of stimulus was required; the animals were no 

 longer disturbed by those extraneous vibrations from the 

 closing of doors and the treading of feet which had produced 

 responses prior to the operation. 



Another animal which had had the ganglion destroyed by 

 painting it with nitric acid, also opened its oral siphon imme- 

 diately (1 minute) after the operation, but kept its aboral siphon 

 closed for some time afterwards. Three days later, both 

 siphons were open and responded to tactile stimulation, but 

 the responses were of an inferior order. 



Two marked changes in the reactions of the animals were pro- 

 duced by these operations on the ganglia: 1) a decrease in 



