RETORT ON THE TUNICATA. 107 



The genital duct is formed of two tidies lying side by side — the oviduct and the 

 vas deferens. They open close together, not far from the atrial aperture, ami close to the 

 outer of two circlets of minute tentacular processes, which projecl from the inner surface 

 ot the cloacal wall close to the atrial aperture (PI. XXIV, tig. 12). These processes seem 

 like a pair of rudimentary diaphragms in the atrial siphon. 



One specimen of this species was obtained in the Southern Ocean, between the Cape 

 of Good Hope and Kerguelen Island, at Station 147; December 30, 1873 ; lat. 40° 16' S., 

 long. 48°27'E. ; depth, 1G00 fathoms; bottom temperature, 0°'8 C. ; bottom, globigeriiia 

 ooze. 



Pol yea rpa, Heller. 



Cynthia, Savigny, Mthnoires sur les Animaux sans Vert&bres. Pt. ii. fasc. 1. 1S16. In part. 



Ascidia, Quoy and Gaimard, Voyage de I'Astrolabe — Zool., t. iii. 1830-34. In part. 



Cynthia, Forbes and Hartley, British Mollusca, vol. i. 1848-53. In part. 



Styela, Hancock, Anat. and Physiol, of Tunieata, Jouin. Linn. Sue. 18G8. In pail. 



Cynthia, Kupffer, Jahresber. der Commias., &c 1875. In part. 



Polycarpa, Heller, Untersuch. ii. d. Tunicaten d. adriat. Meeres., Abth. 3. 1877. 



Polycarpa, Heller, Beitrage zur niihern Kenntniss der Tunicaten. 1878. 



Styela, Traustedt, Oversigt over de fra Danmark, &c, Ascidise Simplices. 18S0. In pail. 



Body attached, sessile, rarely stalked, occasionally incrusted with sand. Bran- 

 chial and atrial apertures either four-lobed or cross-slit. 



Test usually coriaceous, rarely cartilaginous. 



Branchial Sac with four or less than four folds upon each side. 



Tentacles always simple. 



Intestine forming a wide loop. 



Genitalia in the form of a large number of small masses scattered over the inner 

 side of the mantle. 



Heller separated Polycarpa from Styela in 1877, giving as the chief distinguishing 

 features the wide loop formed by the intestine, ami the presence of a large number of 

 small genital glands, to which he gave the name of " polycarps." The close relationship 

 of Polycarpa to Styela has been already discussed (see under Styela, p. 149). 



In external appearance and the nature of the test this genus varies greatly. The typical 

 condition is attached and sessile, with a thin but tough and leathery test, not incrusted with 

 sand. A short stalk is however occasionally formed, as in Polycarpa viridis, by a pr< '^liga- 

 tion of the posterior end of the body, and the test may become thickened and cartilaginous 

 in consistency, as in Polycarpa sulcata. In some species inerusting sand is present in 

 quantities ranging from a few adhering grains, as in Polycarpa radieata, to a complete 

 coatino-, as mPolycarpa tinctor. While finally in Polycarpa molguloides the investment 

 is very thick, and the grains are attached to long delicate hairs as in a typical species of 

 the genus Molgula. 



