346 THE INFLUENCE OF LIVINa SURROUNDINGS. 



visible, while in others the union has proceeded to such a point 

 that even the cell-walls have merged in one. This appears to 

 me to be a very conspicuous deviation from the normal growth 

 of the Ploridese, for, so far as I know, two separate filaments or 

 branches never, or most rarely, anastomose in these marine 

 algiB. Even the absence of all fructification seems to prove 

 that the sea-weed is forced to an illegitimate mode of growth, 

 so to speat, by its association with the sponge. 



But it is, moreover, very probable that the sponge, on its 

 part, is aflfected by the Ploridea. The greater part of its stomata 

 occur only on that side of the broad primary branch which is 

 directed upwards, but sometimes we meet with some which, by 

 a twisting of the branch, have quite lost this normal direction. 

 Now, if the sponge alone could determine the direction of 

 growth, all the mouths would be turned in one direction, and, 

 as this does not occur, the presumption is obvious that this de- 

 viation from its normal behaviour is occasioned by the influence 

 of the sea-weed on the sponge. As it would seem, the direc- 

 tion of growth of the stomata is determined by that of the 

 filaments of the alga ; this extends its blunt tips — which, as is 

 well known, are its growing points — in every direction. They are 

 found everywhere, at the broad free end of the primary branches, 

 as well as within the oldest portion and all round the mouths 

 of the sponge. As the encrusting layer formed by the sponge 

 is excessively thin, it may be supposed that round about the 

 stomata the growth of the sea-weed is as vigorous as that of 

 the sponge, or even stronger ; it is then forced by the filaments 

 of the alga into a direction of growth perhaps not originally 

 natural to it. Be this as it may, in any case the compovmd 

 organism I have here described must be of the highest interest, 

 and I make no doubt that a careful investigation, not of 

 dead specimens, but of living individuals on the spot, with an 

 inquiry into their mode of life and physiological characters, 

 will furnish an answer to the question whether, as I believe, 

 the organisms — sea-weed and sponge — have a reciprocal influence 

 analogous to that which it has been proved that the algse and 

 fungi have in the compound organism known as a Lichen. 



The degeneration of the organs of parasites.— Besides all 



