ASCIDIANS OF THE PHILIPPINES VAN NAME. 



149 



of the object on which it grew, not to any difference of species. 

 Color usually chalky or yellowish white. In specimens from two 

 stations (D5139 and D5154) the upper or free surface of the colony 

 is somewhat mottled with a blackish pigment. The branchial aper- 

 tures of the zooids appear in the contracted preserved specimens 

 as minute depressions, and in some specimens are quite conspicu- 

 ous. Common cloacal apertures are only occasionally recognizable, 

 but are apparently generally rather numerously distributed over the 

 surface. Spicules are abundant in most parts of the colonies, often to 

 an extent rendering the test hard and brittle. 



The spicules are mostly considerably larger than in Didemnum 

 ternatanum, well developed ones averaging 0.027 to 0.038 mm. in 

 diameter, or in some colonies larger (0.04 to 0.05 mm.). They are 

 stellate; their rays rather few and long, regularly tapering in some 



101 lor 



Figs. 98-101. — Didemnum grande (Herdman). 98, Typical spicule. X 700. 99, 

 Common forms op spicules. X 700. 100, Zooid. X 32. 101, Spicules from 



COLONY FROM STATION D5145. X 700. 



colonies, in others usually more nearly cylindrical and truncated at 

 the tip (figs. 98 and 99). 



Zooids greatly contracted in nearly all the specimens so that the 

 determination of their structure is difficult. In their contracted 

 and preserved state they often do not exceed 1 mm. in length; they 

 are numerous and closely placed in the colony. Branchial aperture 

 with 6 small lobes; atrial aperture neither produced into a tube 

 nor provided with a languet. 



Mantle musculature mainly longitudinal, forming distinct bands 

 on the thorax. A muscular process extending into the test from the 

 constricted middle portion of the body is present. 



Dorsal languets apparently arising from the transverse vessels a 

 little way to the left of the median dorsal vessel. 



Stigmata in four rows, rather few in number; in one zooid 9 

 or 10 in a row on each side were demonstrated in the three anterior 

 rows, and 8 in the last or posterior row. 



