ON THE BRITISH SPECIES OF CEISIA, 123 



the clean white appearance of these highly branched parts of 

 the colony and the dirty-brown appearance of the stump of the 

 main stem, covered as it is by foreign growths of various kinds, 

 will give rise to the suspicion that the former have been de- 

 veloped at a later period than the latter, and that the latter 

 are the remains of colonies which developed ovicells at an 

 earlier period of the year. 



Smitt^ has called attention to the fact that the free tubular 

 portion of the zooecium of C. geniculata is sometimes rela- 

 tively transparent, and that it is separated by a sharp line from 

 the basal, more highly calcified part, and he suggests that this 

 transparent portion has in these cases been regenerated. He 

 further points out^ that in Aetea argillacea ( = Aetea 

 truncata, forma abyssicola elongata^) this process of re- 

 generation seems to be periodic, since a zooscium consisting of 

 portions of three different ages was in one case observed by him ; 

 and that in Parrella fusca (=Vesicularia fusca*) the 

 zooecium may attain twice its normal length by the occurrence 

 of this regenerative process.^ Milne-Edwards^ had previously 

 pointed out that the zooecia were able to form rootlets at an 

 advanced period of their existence. 



There can be little doubt that Smitt's suggestion is a correct 

 one. In C. eburnea the older parts of the colony are fre- 

 quently covered with an encrusting red seaweed, the presence 

 of which has no doubt been responsible for the "rose-red" 

 colour which has been mentioned by Johnston'' and others as a 

 feature which sometimes characterises the species. In certain 

 specimens found in April the basal parts of the colonies were 

 completely covered by this encrusting growth, while in various 



» ' Ofvers. af K. Vet.-Akad. Forhandl.,' 1865, No. 2, p. 128. 

 " "Om Hafs-Bryozoernas utveckling och fettkroppar," ' Ofvers.,' &c., 1865, 

 No. 1, pp. 29, 30. 

 3 ' Ofvers.,' &c., 1867, No. 5, p. 280. 



* ' Ofvers.,' &c., 1866, pp. 502, 505. 



* Ibid., pi. xiii, fig. 39, and explanation of figure. 



* ' Ann. Sci. Nat.,' 2« sir., "Zool.," torn, ix, 1838, p. 196. 

 r 'British Zoophytes,' ed. 2, p. 284. 



