COMPOUND ASCIDIANS 



-AMAEOUCIUM. 



587 



nutritive materials it may contain, and carrying away with it any 

 excrementitious matters to be discharged; and this having met 

 the respiratory current in the cloaca, the two mingled currents 

 pass forth together by the Anal orifice i. The long post-abdomen 

 is principally occupied by the large Ovarium, p, which contains Ova 

 in various stages of development. These, when matured and set-free, 

 find their way into the cloaca ; where two large ova are seen (one 

 marked p', and the other immediately below it) waiting for expul- 

 sion. In this position they receive the fertilizing influence from 

 the Testis, q, which discharges its products by the long spermatic 

 canal, r, that opens into the cloaca, ?•'. At the very bottom of the 

 post-abdomen we find the Heart o, enclosed in its pericardium, o\ 

 — In the tribe we are now considering, a number of such animals 

 are imbedded together in a sort of gelatinous mass, and covered 

 with an integument common to them all ; the composition of this 

 gelatinous substance is remarkable as including Cellulose, which 

 generally ranks as a Vegetable product. The mode in which new 

 individuals are developed in this mass, is by the extension of 

 Stolons or creeping stems from the bases of those previously exist- 

 ing ; and from each of these stolons several buds may be put-forth, 

 every one of which may evolve itself into the likeness of the stock 

 from which it proceeded, and may in its turn increase and multiply 

 after the same fashion. A communication between the Circulating 

 systems of the different individuals is kept-up, through their con- 

 necting stems, during the whole of life ; and thus their relation- 



Fig. 303. 



Botryllus violaceus:- 



-A, cluster on the surface of a Fucus : 

 of the same enlarged. 



-b, portion 



