Physiology of some Zoophytes. 391 



provided, towards the mouth (fig. 8«). 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 oesophagus. 

 The particles of carmine sometimes collected in 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. 8 b) 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 I 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)y 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 

 cells 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 ofi". 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 



