LIFE-HISTORY OF TUNICATES 



509 



acquires the power of reproducing asexually, e.g. Clavelina. 

 Both processes are carried further in the compound 

 Ascidians. In these the eggs have usually a considerable 

 amount of yolk, and development takes place either in the 

 atrial cavity of the mother, or in special brood-pouches. In 

 consequence, the development, especially in the early stages, 

 shows considerable modification, although the larval stage 

 is quite distinct. Again, the tailed larva develops into an 

 adult which has no sexual organs, but forms a colony by 

 budding. The individuals of the colony then give rise to 

 eggs and so to larvae. The development thus includes a 

 distinct alternation of generations. 



Fig. 290. — Asexual reproduction in. Salpa. At the Kinder end of 

 the adult endostyle a stolon develops containing tubular out- 

 growths. The stolon breaks out through the test of the adult 

 and becomes constricted to form a series of buds. 



ST., Stolon growing out from ventral surface of parent salp (P.) ; 

 5., S' ., S"., buds at different stages of development. 



Budding takes place in many different ways in the com- 

 pound Ascidians. In one set (the Diplosomidae) the tailed 

 larva is precociously reproductive, giving rise to buds before 

 undergoing metamorphosis. This, forms an interesting 

 transition to the condition seen in Pyrosoma, where the 

 fertilised egg gives rise to a rudimentary larva (cyatho- 

 zooid), from which a young colony of four individuals arises 

 by budding. These individuals again bud, until a large 

 colony is formed, the members of which become sexual. 

 The ova are few in number, a statement which is generally 

 true for the pelagic Tunicates, as contrasted with sedentary 

 forms. 



