406 ARTHUR T. MASTERMAN. 



Structure of Lophophore and Coloration. 

 The anatomy of Plioronis Buskii and that of Pho- 

 ronis austral is, a closely allied species, have been 

 described by more than one worker, and it is here proposed 

 merely to add a few fresh observations to the facts already 

 known. 



Coloration. 



Preservation in alcohol does not appear to affect to any 

 extent the black pigment of Phoronis australis. The 

 arrangement of this is somewhat peculiar. The lophophore 

 or crown of tentacles is banded. Figs. 51 and 52 are dorsal 

 views of the entire animal (natural size). The tentacles 

 appear to be black throughout the greater part of their 

 length, except for a light unpigmented area extending hori- 

 zontally across each coil at about three fifths of the distance 

 towards the base. Another narrower band is found at the 

 base of the lophophore, under which lies the nerve-cord. 

 Pig. 54 is a ventral view of another specimen, in which the 

 white band on the tentacles is seen to extend down to the 

 base of the lophophore, thus meeting the lower band. 



There is, however, considerable variation in the colora- 

 tion, though these three illustrate the general rule. Fig. 54 

 shows an abnormal specimen, in which the whole lophophore 

 is inky black, with no bands. 



The trunk is pigmented for a very variable extent of its 

 length, as is seen by figs. 51 — 54, in which a dotted line 

 indicates the transition from the pigmented to the unpig- 

 mented ai'eas. It is possible that the unpigmented portion 

 is that part which during life was embedded in the skeletal 

 tube of Cerianthus, which also appears to be dark in 

 colour. All the pigment is deposited as minute black 

 granules in the cells of the ectoderm, but whilst the pigment 

 in the trunk is uniformly distributed in the cells, that in 

 the lophophore is confined to the ectoderm of the cubical 

 type, which is found only on one side of the tentacles. 



