CEI-LULAR DEGENERATION AND FORMATION OF PIGMENT. 125 



Black specimens of Sertularia loculosa are not uii- 

 common, but tliey have not been found so frequently as 

 specimens in the non-pigmented condition. 



P a r a g a 1 1 y a intermedia Warren. 

 Text-figs. 10 and 11. 



Hei-e the black condition is not so common as in the species 

 previously discussed, but it was found in material collected 

 at Knysna and at Park Rynie, Natal. 



The blackness is due to the presence of large, rounded, 

 dark brown or black bodies in the ectoderm (text-fig. 10). 

 These black bodies possess considerable depolarising power 

 under crossed Nichols, while the pigment substances of the 

 hydroids previously passed under review do not possess any 

 appreciable influence on polarised light. 



The normal ectoderm of Paragattya intermedia bears 

 numerous large, oval or rounded cells Avhich are charged 

 with radiating elongated bodies of a homogeneous substance 

 appearing to be of the nature of reserve food-material or 

 yolk. In text-fig. 10 the cavity of the blastosphere of the 

 developing planula may be seen to be filled tightly with these 

 yolk-cells. 



In text-fig. 11, E, normal yolk-cells are seen in surface view 

 and in section lying in the ectoderm on the right-hand side 

 of the figure, surrounded by interstitial cells and overlaid 

 by large epithelial cells. In figs, a-d the growth of these 

 cells is illustrated; a-c in optical section, b surface view. 



The black bodies previously mentioned as giving rise to 

 the black condition of certain specimens are derived from the 

 transformation of yolk-cells. Under certain unfavourable 

 stimuli the cells do not form normal yolk-bodies, but 

 a coarse, granular condition of the cytoplasm arises, and 

 the whole substance turns brown (fig. f). The coloration 

 increases, and the cell may become very dark or black. The 

 nucleus appears to swell (fig. G.). Ultimately the cell seems 

 to die, and becomes converted into a rounded mass of homo- 



