THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTOKY. 



[SIXTH SERIES.] 

 No. 46. OCTOBER 1891. 



XXXI. — Note on a Neic and Primitive Type of Compound 

 Ascidian. By Walter Garstang, M.A., Berkeley 

 Fellow of the Owens College, Manchester. 



During some dredging-operations in the neighbourhood of 

 Plymouth, which I have recently been enabled to carry on 

 by means of a Government grant given me by the Royal 

 Society Committee, I met with specimens of a new and 

 interesting Compound Ascidian, which forms the subject of 

 the present note. 



The specimens of this Ascidian were found in moderately 

 shallow water (5 to 15 fathoms) attached to stones and shells, 

 upon which they formed small inconspicuous incrusting 

 colonies, freely coated with sand-grains. The colonies possess 

 a thin, spreading, carpet-like base of test-substance, traversed 

 by stolonial tubes, from which zooids spring up at irregular 

 intervals. Sometimes the zooids are entirely free, but usually 

 they are united into small clumps consisting of several indi- 

 viduals, the tests of which are partially fused together. The 

 zooids project from the basal carpet of test to a variable 

 extent : their height, as a rule, is between 6 and 10 millira. 

 They possess a dilated and somewhat globular thoracic region 

 and an elongated semicylindrical abdominal region, which is 

 always more slender than the thoracic portion. The zooids 

 bear two distinct apertures, the oral and cloacal openings, of 

 which the former is the larger. Each aperture is bounded 

 Ann. & Mag. N. Hist. Ser. 6. Vol. viii. 18 



