THEIR INTERNAL STRUCTURE. 345 



US, bsyond the possibility of doubt, that this body consists of two 

 .distinct organisms, namely, of a sea-weed associated with a 

 sponge exactly as is the case with the lichens among plants, and 

 it is impossible, with only specimens preserved in alcohol, and 

 without investigating their vital properties, to decide whether 

 the form of the whole mass owes its origin to the sponge or to 

 the vegetable growth. The thick and somewhat vitreous, trans- 

 parent branches of the internal network (sse lig. 93), which 

 give rise where they anastomose to the broader branches, on one 

 side of which we find the stomata of the sponge, are un- 

 doubtedly filaments of a sea- weed — probably an undetermined 

 species of Floridea; and the spaces between these internal 

 branches of the sea-weed lead directly into the cavities which, 

 on one side of the main stem, pass into the stomata of the 

 sponge. Hence the margins of these are actually composed of 

 the filaments of the alga. On the other hand, the soft tissue of 

 the sponge proper lies in a very thin layer on each filament ; 

 the sponge has no true fibres, though it has spicula; which are 

 scattered through the soft substance. Unfortiinately the spicultB 

 are so far from characteristic in their structure and their arrange- 

 ment that it is impossible to determine the genus in which the 

 sponge should be systematically placed. If we assume that its 

 normal growth is neither hindered nor modified by its association 

 with the sea-weed, it may with some pi'obability be included in 

 the family of the Ghalinae. 



But it is highly probable that in point of fact both the or- 

 ganisms are to a certain degree reciprocally influenced and 

 modified hy their association. Although I have examined very 

 numerous examples of these colonies, I have never succeeded in 

 detecting the smallest trace of fructification on the filaments of 

 the FlorideiE ; they even seem not to grow in the usual manner 

 of the Floridese, so far as I could determine, and I am supported 

 in this view by those specialists whom I have asked among 

 botanists. In the first place an internal union, by secondary 

 coalescence, occurs between the large primary branches, which 

 continue growing at the ends only ; that they are truly coales- 

 cent and not merely superficially connected is proved by the fact 

 that in many places the original scar or line of contact is still 



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