BRITISH TUNICATA, 



Tribe 2. AGGREGATE * 

 (Compound Ascidia its.) 



Individuals [intimately united, without separate 

 tests, reproducing by gemmation, and forming fixed 

 colonies] wholly immersed in a common envelope. 



Family 5. POLYCLINID.E. 



Individuals much elongated, consisting of a thorax 

 containing the branchial sac, an abdomen containing 

 the digestive organs, and a post-abdomen containing 

 the heart and the reproductive organs ; enveloped in a 

 common mass ; branchial aperture only with lobes. 



[The colony is usually massive, sometimes incrusting, 

 and occasionally lobed or pedunculated ; the systems 

 vary in character, sometimes being imperceptible, and 

 their common excretory orifice is usually inconspicuous; 

 the test is gelatinous or cartilaginous ; the branchial 

 sac is small and not well developed ; the dorsal lamina 

 consists of a series of languets ; the tentacles are few 

 and small.] 



* Additions to the authors' MS., except obvkrasly editorial foot-notes, are 

 placed within brackets, as in the previous volumes of this work. The term 

 " common body," with which the description of each genus and species com- 

 menced, is altered to " colony " ; the term " rays," for the divisions of the 

 branchial aperture, to " lobes " ; and the term " anal," when applied to the 

 aperture of the atrium, to " atrial." Approximate dimensions in milli- 

 metres are inserted. A few corrections to references, verbal alterations, 

 and transpositions are not indicated. 



III. 1 



