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the water. This resulted in the great enlargement of these 

 cavities and the development in the body-walls of transversely 

 placed bands of muscle which served to drive out with force 

 the contained water. The posterior region of the body, 

 or tail, being now superseded as an organ of locomotion, 

 became suppressed, and thus the Thaliacea {Salpa, &c.) were 

 evolved. 



In the second ancestral line the animal changed its 

 habits, and became sessile ; and, just as we find the tailed 

 larval Ascidian at the present day, after a short free-swim- 

 ming existence, becomes attached, loses its locomotory organ, 

 and undergoes other changes, so the ancestral Tunicate, when 

 it settled down on some object to lead a stationary existence, 

 went through a similar but gradual process of degeneration. 

 The tail, with its contained notochord, being no longer 

 necessary, became rudimentary and disappeared. The well- 

 developed sense organs, which were most important to a 

 locomotory organism, had become almost useless through 

 the change of life, and they also became suppressed, and, as 

 a result, the nervous system, which was in most intimate 

 connection with the sense organs, underwent considerable 

 degeneration. On the other hand, the alimentary canal, and 

 especially its respiratory portion, became greatly enlarged 

 and somewhat complicated. This resulted in the formation 

 of an ancestral form somewhat resembling the Simple Asci- 

 dians, and probably more like a solitary Clavelina than any 

 other existing form. It is probable that this creature then 

 acquired the power of reproducing by gemmation, so as to 

 form small colonies, like those of the " Social " Ascidians 

 (Clavelinidse). From this point two lines started. In one 

 series of ancestors the power of budding was retained, and 

 the members of the resulting colonies became more closely 

 united. This led up to the Compound Ascidians, which 

 have branched out into many smaller groups. The other set 



