TWO NEW SPONGILLxE FROM LAKE TANGANYIKA. 475 



papillosa, SoUas, 1879) [11], there are branched spicules in 

 which the axial threads are continuous throughout, a fact which 

 may indicate that the spicules themselves owe their form to 

 branching. It seems clear, therefore, that the irregular 

 spicules of Spoil gill a moorei have in many cases been pro- 

 duced by fusion. Judgment must be suspended for the 

 present with regard to those systems in which no discontinuity 

 can be detected in the axial threads of the component spicule 

 rays ; such spicules may be simply branched. The question 

 cannot be decided until the actual origin of the spicules has 

 been studied, and the same may be said for Tricentrium. 

 Since now it has been shown that the triradiates and quad- 

 radiates of the Ascons are formed by fusion, there is no 

 inherent improbability in a similar process occurring in other 

 cases [8]. 



Spicules of a similar character to the compound systems here 

 described have been figured by many authors in various Spon- 

 gillidse (Spongilla aspinosa, Potts [9]; Lubomirskia 

 intermedia,, Dybowski [4]). All these authors regard them as 

 abnormalities, but in moorei they are so frequent that they 

 must be considered as a normal feature of the species. It is 

 possible that in other Spongillidse these systems have not 

 received the attention they deserve. 



In addition to the spicules described above, there are small 

 masses of silica in Spongilla moorei, comparable with those 

 found in Spongilla aspinosa (PI. 37, fig. 5). 



(b) The Arrangement of the Spicules to form 

 Fibres, &c. — The spicules which form the polyspiculous 

 fibres belong mainly to the first and third classes above 

 described. Spicules of the first class form the greater part of 

 the fibres, while others lie about in the sponge tissue, 

 presenting for the most part an irregular method of arrange- 

 ment, though many such spicules are placed so as to bridge 

 over the spaces between the fibres in a perfectly definite way. 

 Spicules of the second class, which are far less numerous than 

 those of the first, seldom participate in the formation of the 

 fibres, but, as a rule, lie scattered irregularly between the 



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