420 DR S. F. HARMER AND DR W. G. RIDEWOOD ON THE 



such a colony would snap off several of the upright pieces, but would not dislodge the 

 basal plate. This view of the constitution of the colony is supported by the fact that 

 the diminutive colony of C. sibogae is composed of a basal encrustation growing on a 

 stone, and a series of upstanding pieces (05, p. 13, and pi. i. fig. 2). 



EXTERNAL APPEARANCE OF THE ZOOIDS. 



The Scotia specimens are, unfortunately, in a rather poor state of preservation. 

 In many cases the zooids had obviously retreated, on being killed, into the deeper 

 recesses of the ccencecium, where they did not come properly into contact with the 

 preserving fluid. The result is that they are usually in a highly and often very 

 irregularly contracted state, and their tissues are a good deal macerated. They are 

 frequently in closely aggregated and deeply pigmented masses, which have somewhat 

 the appearance of the zooid with its buds of C. nigrescens shown by RIDEWOOD (07 ', 

 pi. iii. fig. 7). They are, in fact, more similar in external appearance to the zooids of 

 that species than to those of any of the species of Demiothecia previously described. 

 In well-extended and fairly straight individuals the average length from the end of the 

 metasome to the free ends j of the arms is 4'5 mm., the length from the end of the 

 metasome to the bases of the arms about 3 '2 mm. The thickness of a zooid is 

 about "8 mm. 



The zooids are, however, probably all shorter than they would have been in their 

 fully extended condition, since the wrinkling of the skin indicates a strong contraction 

 of the muscles, particularly of the longitudinal muscles of the anterior side of the 

 metasome and of their continuation into the stalk. 



All parts of the epidermis contain a dark pigment, so that the zooids have a deep 

 brown or black colour in the preserved material. It is obvious that the pigment is 

 not completely dissolved out by alcohol ; but it is probable that its diffuse arrangement, 

 as seen in the preserved specimens, does not represent the exact disposition during life. 

 This is suggested by the comparison of sections of certain individuals of C. nigrescens 

 (Discovery Expedition) which had been preserved with special care with sections of 

 zooids which had not been so treated (see also p. 426). The former series show pigment- 

 granules in sharply restricted areas (cf. RIDEWOOD, 07 1 , pi. v. fig. 28), while the latter 

 show a diffuse arrangement, suggesting that the pigment had been partially dissolved 

 out, and then redeposited as a general staining of the tissues. 



PROBOSCIS. 



The proboscis or buccal shield of the zooids in the material brought back by the 

 Scotia is in such a poor state of preservation that it is not possible to make a state- 

 ment as to its average shape and size. By an examination of whole zooids under a 

 dissecting microscope, sufficient can be seen to show that the proboscis offers no 

 exceptional features ; there is a main lobe, and a lower lobe, thinner than the main 



(ROY. soc. EDIN. TRANS., VOL. XLIX., 544.) 



