ON THE BRITISH SPECIES OF CRISIA. 141 



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 zooecium consisting of 

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

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

 zocEcium may attain twice its normal length by the occurrence 

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

 pointed out that the zocecia 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. Forbaudl.,' 18G5, No. 2, p. 128. 



2 "Om Hafs-Bryozoeriias utveckliiigocli 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* ser., " Zool.," torn, ix, 1838, p. 196. 



7 ' Biit.isli Zoophytes,' ed. 2, p. 284. 



