14 THE VOYAGE OF H.M.S. CHALLENGER. 



says the lichens are also nothing but fungi and algfe together ; still, they form a systemati- 

 cally independent subdivision, owing precisely to their double nature. I do not know 

 whether botanists are right in separating systematically the lichens, l)ut this question is of 

 no consequence to us ; I do not, however, believe the comparison just mentioned to be 

 fortunate. The lichens represent an extreme instance of that kind of symbiosis which 

 v. Beneden caEs " mutualismus." The symbiosis of filaments with sponges is even not so 

 much a commensalism as an indubitable parasitism. In the case of mutualism, the beings 

 constituting the whole undergo such modifications in their structure that a separate 

 existence becomes impossible. There are to be found no deviations in the organisation of 

 sponges attacked by filaments, as compared mth that of closely allied forms devoid of 

 them. Microscopic preparations of Hircinia variahilis and Cacospongia scalans show no 

 differences apart from the presence and absence of filaments. There are, accordingly, 

 absolutely no grounds for supposing that Hircinia, having got rid in some manner or 

 other of filaments, would be no longer able to live. It is also quite obvious that the 

 phenomenon under consideration is not commensalism, but parasitism. Beginning with 

 forms like the Challenger specimen of Cacosjwngia coUectrix, where filaments are repre- 

 sented but very scantily, we come through all possible intermediate stages to the forms 

 which, as in the case of the Challenger specimen of Cacospongia irregularis, are so 

 overloaded with them that the parenchyma is almost entirely replaced by these 

 curious organisms ; all this, now that the independence of the filaments is no longer 

 doubtful, seems to me a decisive proof in favour of the opinion held for many years 

 by Carter, that in the filaments we have really to do with nothing but parasites. 

 This conclusion alters the matter. There are instances in which the diagnosis of 

 parasites involves the mention of the host they inhalnt. This does not occur, however, 

 except in connection with certain modifications in the structure of the parasite, 

 rendering it impossible for it to inhal)it anotlier host ; but nobody would characterise 

 the host systematically by reference to its parasites, and should we adojjt the family 

 of Hircinidse as a fiimily represented by forms witli filaments in the parenchyma, we 

 should be equally obliged to subdivide the species Homo sapiens, according to the 

 presence or al^sence of Tcenia solium, into two systematic groups. Hence I propose the 

 dissolution of the family Hirciuidse, and the location of its representatives in other 

 groups, according to more positive characters. 



The question as to the nature of the filaments, whether j)lauts or animals, is therefore 

 beyond the domain of spongiology ; but since it is of great general interest, I 

 venture to communicate here what I was able to make out in this direction durina: the 

 examination of the Challenger material. As to their structure, I must refer the reader to 

 the statements of F. E. Schulze. I was able to discern all he has seen, but was unable 

 • — in spite of the excellent homogeneous immersion system (^) of E. Winkel — to make 

 out anything more as to their organisation. The comparative size and shajie of the heads 



