DESCRIPTION OF EPHTDATIA BLEMBINGIA. 75 



the deeper tissues, and which present a kind of basket- 

 shaped form. 



(c) The last class of spicules to be considered consists of 

 the amphidiscs (PI. 1, fig". 4, b). The diameter of the hat- 

 shaped disc is about three times that of the shaft. The two 

 discs are exactly similar in size and shape. The surface 

 situated away from the shaft is smooth and convex, while the 

 other surface is concave. Their margins are very finely 

 serrated. The shaft is covered with spines which are conical 

 in shape and placed at right angles to the axis of the amphi- 

 discs. 



In addition to the fully mature forms, all the stages of 

 development are represented, from the simple rod slightly 



fact that, if the supposition here made were true, it would cut at the very 

 root of the system of division into sub-families, now adopted, of the so-called 

 Spongillidae, tlie reasons given above seem to be sufficiently weighty to compel 

 us to lay aside this possible view of the nature of these enigmatical bodies. 



The second supposition that suggests itself as a solution of the problem is 

 that these structures are a kind of symbiotic or parasitic sponge. This 

 supposition is not so unreasonable as it would at first appear, for we already 

 know that SpongiUa bolunii is parasitic on Spongilla nitens (17). Be- 

 sides, it must be remembered that all the spicules in connection with these 

 bodies are quite different from those which form the sponge skeleton, being, 

 as has been stated already, only half as long and less than half as thick. It 

 is no argument to say that they are incompletely developed, for they are all 

 of equal size, which would not be tiie ca?e il they were merely young spicules. 

 However, if these bodies are of the nature of a parasitic sponge, there are, at 

 present, no data by which its position among the Spongillidse can be determined. 



There is still left another possible solution of the problem, namely, that the 

 bodies here discussed are the result of parasitism on the part of some animal 

 other than a parasitic sponge. If this supposition were true, these bodies 

 would have to be considered as a kind of gall, by means of which the sponge 

 endeavoured to protect itself from the action of an unwelcome intruder. But 

 there are two facts which go against this view. In the first place, though I 

 have examined several of tiiese bodies, 1 have so far failed to find any animal 

 inside them. In the second place, though there are many parasites in the 

 sponge, not one of them has as yet been found to possess such a coat as these 

 bodies would provide. 



Though it must be left an open question what the nature of tiiese bodies 

 are, for the reasons given above I an) inclined to adopt the view that they are 

 parasitic sponges. 



