104 ERNEST WARREN. 



The manner of the production of the pigment or coloured 

 substance and the kind of cells affected vary in the different 

 species, but in all cases the whole or a portion of the cell 

 producing it dies, and more frequently the colony appears to 

 be in a somewhat weak and sickly condition, although not 

 necessarily moribund. 



The Causes of Pigmentation. 



The material at my disposal, and the lack of opportunity 

 for extended observations ou the sea-shore, preclude any final 

 statement as to the cause or causes of the phenomenon. There 

 is, however, some evidence for suggesting that excessive 

 insolation is one of the agents in inducing the pigment- 

 degeneration in the cells. Another factor which certainly 

 favours it, and perhaps at times is sufficient in itself, is the 

 senescence of the colony. A third possible cause is the 

 continued stimulation of the colony by the agitation of 

 the water between the tide-marks, and another conceivable 

 factor is the stimulus arising from the partial dessication 

 Avhich may periodically occur when colonies are left exposed 

 by the receding tide. As far as my observations go, the 

 coloured colonies appeared to be especially those which were 

 of considerable age and which happened to be exposed to 

 the direct sunlight and to the buffeting of the waves. The 

 material examined was mostly obtained from the rocks 

 between the tide-marks, and the few specimens collected by 

 ti'awling in deep water belonged to species in which pigment- 

 degeneration has not been observed. It would be of interest 

 to compare specimens of the same species collected on the 

 shore and from deeper water in order to estimate the effect 

 of insolation. 



Senescence of the colony would, however, appear to be an 

 undoubted factor. Old and large colonies tend to exhibit 

 the condition in a far more striking manner than young, 

 small colonies. The young, growing parts of an old, niciture 

 colony may show considerable pigmentation, and it would 

 therefore appear that the vital activity of the colony as a 



