DEGENERA TION. 39 



habit of life. We may now proceed to look at 

 some sessile or immobile animals which are not 

 usually regarded as degenerate, but which, I think, 

 there is every reason to believe are the degenerate 

 descendants of very much higher and more elaborate 

 ancestors. These are certain marine animals, the 

 Ascidians, or sea-squirts. These animals are found 

 encrusting rocks, stones, and weeds on the sea 

 bottom. Sometimes they are solitary (Fig. 13), but 







FiG._ 13. — Two adult Ascidians: to the left Phallusia— to the right Cynthia: the 

 incurrent and excurrent orifices are seen as two prominences. Half the natural 

 size. 



many of them produce buds, like plants, and so 

 form compound masses or sheets of individuals 

 all connected and continuous with one another, like 

 the buds on a creeping plant (Fig. 14). 



We will examine one of the simple forms — a 

 tough mass like a leather bottle with two openings ; 

 water Is continually passing in at the one and out at 



