W. H. HARRIS ON MARINE MICROSCOPIC VEGETABLE ORGANISMS. 145 



fied; a fiinge of mineral matter surrounds the outline of the 

 plant and is a very satisfactory exposition of this method of 

 adapting itself to its environment. 



Whichever form of communication the various species may 

 adopt, there can, I think, be very little doubt as to the purpose 

 such communications serve in the economy of the plants. Their 

 function appears to me to be threefold : primarily for the imbibition 

 of water necessary to the growth of the organism ; secondly, for 

 the escape of gas which must be evolved during the process of 

 excavation ; thirdly, where organised apertures are present, as 

 excretory ducts for the liberation of reproductive bodies which 

 form within the filaments. 



I am not aware that very much more than the foregoing is 

 known regarding the physiology of these plants. Experiments in 

 this direction could be, prosecuted only by any one having access to 

 a marine laboratory, and even then it would be quite impossible 

 to reproduce the conditions under which some of the species 

 appear to fiourish. We are therefore obliged to confine our 

 investigations to the cavities they have eroded, for the remains 

 which are present are of such extreme tenuity, so utterly devoid 

 of structure, and so persistently refuse to respond to the action of 

 reagents, that no progress can be made. I am fully alive to the 

 fact that mere external form unaccompanied by structural 

 description may be misleading, but unfortunately it is the onh' 

 means at present known whereby species may be discriminated. 

 I have, therefore, endeavoured to minimise the errors such a 

 course is open to by collecting many specimens of each form, not 

 only from the dredging in which the original was found, but also 

 from material from widely separated areas. When, therefore, 

 certain characteristic forms are persistent I think we are justified 

 in regarding them as indicative of specific value, at least until 

 more reliable means are known to guide us to a safe conclusion. 



By a slow process of decalcification their remains can be 

 disengaged from the shells ; but beyond obtaining a very thin 

 pellucid film agreeing exactly with the conformation of the cavity 

 no results have accrued by so doing. They are exceedingl}* 

 fragile, and break up into an irrecognisable mass with the 

 slightest pressure. 



Sometimes the cavities are filled with a yellowish -brown 

 plasmic substance; in some specimens this has a tendency to 



