COMPOUND ASCIDIA. 163 



the next place penetrated by two orifices in the upper surface, fig. 21. 

 The yellow spinula so active on bursting its integument, has been now 

 converted to a stationary ascidia, adhering ever after by the front of the 

 head metamorphosed to a circular base. 



All these transitions are rapid. While still in full activity, the head 

 of the spinula seems enlarging ; when motionless, its clefts are extending 

 as roots amidst a thin diffusing grey substance, which soon disappears. 

 Meantime the extending roots remain connected by a very slender com- 

 munication with the central nucleus. Two orifices with sensible contrac- 

 tion and dilatation open above ; the diffusing matter below continues 

 scarcely perceptible ; and some interanea may be obscurely discerned 

 through the integument of the under surface. Within ninety hours of the 

 bursting of the prolific capsule from the large and shapeless specimen of 

 the Botryllus, the metamorphosis of the spinula was perfected. 



The observations detailed at length in the preceding chapter, will aid 

 the explanations given here. I had got the specimen on October 3 ; the 

 first ova and spinula; appeared on the 9th. Some of the latter, at this time 

 escaping from the integument, were perfected as ascidise on the 17th. 

 Each of these animals formed a spherical segment with two wide orifices, 

 whither buoyant particles were attracted and absorbed, obviously passing 

 to the intestinal canal. Thence they were ejected as dark pellets or cylin- 

 drical excretions, like those discharged by the numerous creatures in matu- 

 rity composing the parent mass. The pulsation of a large vessel or heart 

 below was distinctly seen through the ftecal orifice ; and the distribution 

 of the sanguiferous fluid by many channels. 



Herein is again to be witnessed a fact of peculiar interest to the 

 physiologist, a branch of that important system in the animal economy 

 which was lately described. This pulsation still continues perceptible 

 when the young ascidia is three weeks old ; dark particles are visibly car- 

 ried along with considerable force by fluid currents, and transmitted to the 

 place of their destination within the body. The extremities of the radicles 

 have enlarged, while the intermediate portion or neck nearer the ascidia 

 has diminished. But the dark particles are sensibly conveyed through 

 channels traversing the neck. 



