Cutleria multi fida (Grev.). 107 
characters of the fasciated shoot ; variations in this point 
being still considerable, giving rise to growth-forms which 
have been regarded as varieties ; those with a lesser degree 
of fasciation being extremely common, especially in localities 
where external conditions are unfavourable. (Orkney ; cp. 
C. penicillata , Lamour ; C. penicillata , Kutzing). 
(2) It is now the only character left which has not been 
observed in cultures, and it would therefore appear to 
demand the most delicate adjustment of external assimilative 
conditions. 
Considering the three types from the standard of attainment 
of this assimilative growth-form, it would appear that C. mul- 
ti fida, which covers the widest range of temperature in dis- 
tribution, presents these specializations in a high degree in 
its sexual shoot, but maintains existence under conditions 
unfavourable to its development by reduction to a degenerate 
creeping Battersia- like form, which alone persists at the 
extreme northern limit of distribution. 
C. adspersa , with a considerably narrower range of distribu- 
tion, exhibits a thallus, meagre by comparison with C. multifida , 
but more dorsiventral. Its Aglaozonia- stage, suggested for 
A. chilosa by Falkenberg, has not been more definitely 
isolated ; but Janczewski showed that the foot-embryo passed 
directly into a dorsiventral disc on the approach of summer 
at Antibes. 
Finally, in Zanardinia collar is the fasciated shoot, with 
extreme dorsiventral development, becomes itself prostrate, 
and by vegetating in the manner of an Aglaozonia- disc in 
the hot summer does away with the necessity for such a basal 
formation from the embryo ; and thus, being itself homotypic 
and obtaining the perennating advantages of the procumbent 
growth-form, presents the paradox of becoming degenerate 
by carrying to extremes the last variation of the family. 
During a portion of the time in which these observations 
have been made, the writer has occupied the Oxford University 
Table at the Laboratory of the Marine Biological Association 
at Plymouth ; and in acknowledging the goodwill and unfailing 
