ANATOMY AND DEVELOPMENT. l8l 



For convenience, the Ascidians, as a whole, may be 

 arranged as follows: — 



SESSILE ASCIDIANS. 



The compound sessile Ascidians consist of colonies of 

 individuals or ascidiozooids produced by budding from a 

 parent individual. Such colonies are often brilliantly 

 coloured and of massive proportions, as Amaroiiciinn and 

 Fragarium. Others form thin encrusting expansions on the 

 surfaces of marine plants and shells, as Botryllus dsid Lcpto- 

 cliniim. In others, again, the individuals are entirely 

 separate, except at the base, where they are connected 

 together by a common creeping stolon from which new 

 buds are periodically produced, as Clavelina and Peropliora. 



STRUCTURE OF A SIMPLE ASCIDIAN. 



Test, Mantle, Atrium, Branchial Sac. 



The simple or solitary Ascidians which do not produce 

 buds, present hardly less striking differences among the 

 different families than do the compound, but their general 

 shape is much more uniform. 



