The Tunicates, or Ascidians 



479 



The Salpas abound in the warm seas, the chains often cov- 

 ering the water for miles. They are perfectly transparent, 

 and the chains are often more than a foot 

 in length. In Doliolum the body is barrel- 

 shaped and the gills are less modified than in 

 Salpa. The alternation of generations in 

 this genus is still more complicated than in 

 Salpa, for here we have not only a sexual 

 and a non-sexual generation, the individuals 

 of which differ from each other, but there 

 is further a differentiation among the asexu- 

 ally produced individuals themselves; so 

 that we have in all three instead of two sorts 

 of animals in the complete life cycle. Besides 

 the proliferating stolon situated on the ventral 

 side, the bud-producing individual possesses a 

 dorsal process larger than the stolon proper. The buds become 

 completely severed from the true stolon at an early stage and 



FIG. 286. Botryllus 

 ma gnus Hitter, a 

 single Zooid. Shu- 

 magin Islands, Alas- 

 ka. (After Hitter.) 



FIG. 287. Aplidiopsis jordani Ritter, a compound Ascidian. Lukanin Beach, 

 Pribilof Islands. (After Ritter.) 



actually crawl along the side of the parent up to the dorsal 

 process, upon which they arrange themselves in three rows, 

 two lateral and one median. The buds of the lateral rows 

 become nutritive and respiratory zooids, while those of the 



