322 CEYLON PEARL OYSTER REPORT. 



of the body-wall, and from the blood lacunee, might take up nutrient particles brought 

 in by the water and ingest and digest them in an intracellular manner. Although, 

 in the absence of the branchial sac, there can be no strong current through the 

 animal, still the muscles of the mantle, and especially the sphincters of the siphons, 

 will no doubt suffice to draw in and to expel supplies of water, and the cilia of the 

 peripharyngeal bands and of the tentacles will be able to separate out, guide, and 

 retain the diatoms and other nutrient particles. 



If the food can be brought within reach of the amcebocytes and ingested, there is 

 probably no difficulty in regard to digestion. Such cells are probably able to form 

 the necessary ferments and effect solution and absorption of the food. It is known 

 that ordinary tissue-cells in even a higher animal contain erepsin, and possibly other 

 ferments, and can exercise a slow proteolytic action. It seems highly probable* that 

 leucocytes and other undifferentiated cells especially in plastic organisms like the 

 Ascidians, where tissue differentiation is not highly marked contain amylolytic and 

 proteolytic ferments sufficing for intra-cellular digestion of microscopic organic food. 



Polycarpa sluiteri, n. sp. Plate V., figs. 16 to 21. 



External Appearance. Shape pyriform or oblong with a narrower anterior end 

 terminated by the branchial aperture. Atrial aperture half-way down dorsal edge 

 (fig. 16). Surface rough, corrugated, having a few shell fragments and other foreign 

 bodies adhering. Attached by posterior end and parts of left side. Colour, very dark 

 grey, nearly black in places. Size, 3 centims. x 2 centims. x 1'5 centims. 



Test tough and leathery, rough and irregular on outer surface, quite opaque, 

 smooth, but rather dark on the inner surface and grey in section. 



Mantle dark coloured, not thick, with strong muscular siphons. 



Branchial Sac with four wide folds on each side, with about nine or ten bars in the 

 folds and five rows of stigmata in the interspace. Transverse vessels alternately 

 larger and smaller. Meshes square, containing each seven or eight rather long narrow 

 stigmata (fig. 21). 



Dorsal Lamina a plain membrane with no ribs and no marginal teeth. 



Tentacles of two sizes, six very large and six much smaller. 



Dorsal 'Tubercle rather small and slight, in a deep narrow triangular peritubercular 

 area, with the opening anterior and the horns turned one in and one out but not 

 coiled (fig. 17). Two other tubercles are shown in figs. 18 and 19. 



Gonads numerous; from 15 to 20, dull yellow, sausage-shaped polycarps on each 

 side of the body, arranged roughly in a row facing the atrial aperture (fig. 20). A 

 few dark-coloured endocarps projecting between them. 



Locality: (l) Station V., Chilaw Paar, 10 fathoms, three specimens ; (2) Aripu 

 coral reef, one specimen. 



This species in some respects resembles Polycarpa mutilans, but differs from it so 



* In the light of recent work by Ascoli and Mareschi, Vernon, Rulot, and the Ladisls. 



