CKLLULAIi DEGENERATION AND FORMATION OF PIGMENT. 113 



(2) Thuiaria tubulif oriiiis {31. -Turn.). 

 PI. XII, figs. 4, 5 ; text-figs. 4, 5. 



This hydroid is one of the commonest on the Natal coast. 

 ]t is abundant in tlie form of small, short colonies attached to 

 the bare surface of rock. In certain situations the colonies 

 are left exposed to the air for some time during low-water. 

 As a matter of fact, this species is subjected more mai-kedly 

 than any other to : (1) intense insolation, (2) periodical 

 buffeting by the waves, (3) periodic partial dessication. I 

 have not been able to separate satisfactorily the effects of 

 these various agents ; but there is no doubt that unfavourably 

 placed colonies are particularly liable to pigment-degenera- 

 tion. 



In PI. XII is shown the general aspect of a portion of a 

 colony in which the degeneration is beginning (fig. 4) and in 

 which it is in an advanced condition (fig. 5). 



The natui'e of the pigment-degeneration differs appreciably 

 from that described in Lytocarpus filamentosus. The 

 degeneration is less confined to individual cells than in that 

 species. A group of cells or portions of cells becomes involved 

 and there are formed elongated masses or narrow streaks of 

 vacuolated, blackened material extending through the living 

 tissue. 



The degeneration first begins by the formation of pigment 

 granules enclosed by a mucilage-like layer. When a number 

 of granules are formed close together there results a soft 

 unstainable (e. g. with carmine and hsematoxylin) patch in 

 the cytoplasm crowded with dark brown or black pigment 

 granules. These granules ai'e much smaller than in Lyto- 

 carpus, being about half the size. They are also much 

 blacker, and consequently far more opaque and less refringent 

 (text-fig. 4, d) . The protoplasm of the cell becomes con- 

 spicuously vacuolated and honeycombed and the granules 

 accumulate around the walls of the cavities, forming a dense 

 black edging. Text-tig. 4, j-m, I'epresents the changes in a 

 VOL. 4, PART 1. 8 



