Ascidians

Ascidiæ simplices, or simple Ascidians, comprise solitary and social forms, the latter united by branched IMG:content-0330.png:[graphic][graphic][merged small][merged small][subsumed][subsumed][merged small] root-proce es. The testa of the former is warty and opaque, of the latter hyaline, like cartilage. Clavellina represents the latter, and Ascidia or Cynthia the former. A. composite are small forms united in ma es by a common mantle, and having a sponge-like or incrusting appearance. In Botryllus the individuals are grouped in star-like clusters about a common exhalent orifice. A. salpæformes are free-swimming, thimble shaped colonies, the hollow of the thimble serving as a common exhalent osculum. The egg develops, in an ovarian sac, into a cyathozoöid which in turn produces, by budding, four ascidiozoöids (sexual forms). These produce the colony by budding from a stolon at the hinder end of the endostyle; and each individual zoöid, as it develops, contains one egg. Pyrosoma (named from its phosphorescence) represents this order.