ASCIDIANS OF THE PHILIPPINES VAN NAME. 



153 



canals can be traced by slight furrows or darker lines on the surface, 

 in others there are no such indications of them. 



• Spicules noteworthy for their smallness in most specimens, gen- 

 erally ranging from 0.008 to 0.028 mm. in diameter. In some colo- 

 nies the larger spicules will scarcely average over 0.01 mm. in di- 

 ameter ; in others they may average 0.02 mm. or even more. In some 

 colonies from station D5136 the spicules are unusually large, many of 

 them measuring 0.03 mm. or over. In form they are usually better 

 described as burr-like rather than stellate, on account of the large 

 number of points or rays with which they are provided, or, more 

 strictly speaking, of which they are composed, but in some colonies 

 the prevailing type of spicules has fewer rays. The points are often 

 narrow and sharp 

 (though they never ex- 

 hibit the regularity and 

 perfect conical form 

 that is frequent in some 

 members of this genus), 

 but in most . colonies 

 they are mostly irregu- 

 larly blunted at the tips 

 and often so short that 

 the spicule has nearly a 

 spherical form (see fig. 

 105). Spicules gener- 

 ally very numerous in 

 the surface layer of the 

 test, becoming less nu- 

 merous and disappear- 

 ing entirely in the deep portions of the colony, where (beneath the 

 zooids and the cloacal canals) the test is solid and translucent 

 though rather soft and easily torn. Some colonies, however, have 

 few spicules, even in the superficial parts. 



Color of the alcoholic specimens generally buff, often with a 

 purplish tinge or some shade of purplish brown or light brown, but 

 many of the specimens have the superficial layer of the upper surface 

 darker, due to the presence of rather large pigment cells in this layer. 

 These are occasionally so numerous and deeply pigmented as to give 

 the upper surface a dark-brown color (very dark in two colonies from 

 station D5144). In some conspicuously pigmented colonies the edges 

 of the colony and the border of the large common cloacal aperture 

 or apertures are practically free from pigment and are light colored, 

 in more or less conspicuous contrast to the rest of the upper surface. 

 The minute closely placed branchial apertures of the zooids are usu- 

 ally quite conspicuous on the surface. Large elongated and irregu- 



Figs. 10i-106. — Didemnum ternatandm (Gott- 

 schaldt). 104, Spicules from a colon y from 

 Uldgan Bay. x 700. 105, Spicules from a col- 

 ony from Station D5136. X 700. 106, Zooid. 

 X 25. 



