Physiology of some Zoophytes. 391 
provided, towards the mouth (fig. 8a). At this part all the cur- 
rents converge, and thus produce an upward central current, by 
which the particles of carmine are carried outwards. None of 
the carmine, as far as I could observe, entered the cesophagus. 
The particles of carmine sometimes collected im considerable 
masses around the mouth before they were floated outwards. As 
the termination of the intestine opens near to the mouth, and at 
a point within the influence of this outward central current, the 
egesta when voided are rapidly carried away. It would thus ap- 
pear that when substances not fitted for the nourishment of the 
animal are conveyed towards the mouth, the walls of this aper- 
ture are endowed with a specific property of irritability by which 
they are thrown into contraction and prevent its entrance. Such 
substances on the other hand as are capable of nourishing the ani- 
mal do not act as excitants to this property of contractility, and 
they may be carried inwards. The possession of such a property is 
probably necessary for the existence of the animal. In this ani- 
mal, as is well-known, the whole digestive tube and the ciliary 
motions on its inner surface can be distinctly seen through the 
transparent body. The walls of the stomach (fig. 84) and the 
first portion of the intestine (duodenum *) (fig. 8 c) are very much 
thicker than the rest of the digestive tube, and were never ob- 
served to contract ; and this last circumstance, viz. the non-con- 
tractility of these parts of the digestive tube, does not exist, as far 
as [ am aware, in any other ascidian polype. A slight contractile 
movement was observed in a few cases at the upper part of the 
gullet. The last part of the intestine (fig. 8 d), which is not pro- 
vided with cilia, contracts and expels the egesta which have pre- 
viously accumulated there, frequently in considerable quantity. 
Brownish masses, apparently chiefly composed of the granules and 
eells which so abundantly line the inner surface of the stomach, 
are frequently seen in rapid rotatory motion in the stomach and 
duodenum. 
The life of the body is of shorter duration than that of the 
stalk, and I have observed in several specimens the body fade and 
fall off, and a new one reproduced in its place, A few days be- 
fore this takes place, the tentacula are permanently bent inwards 
and the membrane surrounding their lower part remains con- 
tracted, so as to completely, or nearly completely, cover the upper 
surface of the body, presenting in fact the appearance which the 
animal temporarily assumes when disturbed. The body then 
becomes more opake and at last falls off. After this the stalk 
retains its property of alternately contracting and relaxing its 
different surfaces at intervals, upon which its movements depend. 
After the lapse of a few days the top of the stalk enlarges, and a 
minute head presents itself in which the different parts of the 
