38 PORIFERA 



made a new departure in the field of experiment by feeding 

 sponges with coloured solutions, and obtained valuable results. 

 Thus solutions, if presented to the sponge in a state of extreme 

 dilution, are subjected to choice, some being absorbed, some 

 rejected. Wlien absorbed they are accumulated in vacuoles 

 within both dermal and gastral cells, mixed solutions are separ- 

 ated into their constituents and collected into separate vacuoles. 

 In the vacuoles the solutions may undergo change ; Congo red 

 becomes violet, the colour which it assumes when treated with 

 acid, and similarly blue litmus turns red. The contents of the 

 vacuoles, sometimes modified, sometimes not, are poured out 

 into the intercellular gelatinous matrix of the dermal layer, 

 whence they are removed partly by amoeboid cells, partly, so 

 Loisel thinks, by the action of the matrix itself. It adds to the 

 value of these observations to learn that Loisel kept a SiJongiUa 

 supplied with filtered spring-water, to which w^as added the 

 filtered juice obtained from another crushed sponge. This 

 Spongilla lived and budded, and was in good health at tlie end 

 of ten days. 



Movement. — Sponges are capable of locomotion only in the 

 young stage ; in the adult the only signs of movement are the 

 exhalant current, and in some cases movements of contraction 

 sufficiently marked to be visible to the naked eye. Meresjkowsky 

 was one of the early observers of these movements. He mentions 

 that he stimulated a certain corticate Monaxonid sponge by 

 means of a needle point : a definite response to eacli prick inside 

 the oscular rim was given by the speedy contraction of the 

 osculum.^ 



Pigments and Spicules. — Various reasons lead one to con- 

 clude that tlie spicules luu'e some function other than that of 

 support and defence, probably connected with metabolism. For 

 the spicules are cast off, sometimes in large numbers, to be 

 replaced rapidly by new ones, a process for which it is difficult 

 to find an adequate explanation if the spicules are regarded as 

 merely skeletal and defensive.^ Potts remarks upon the strik- 

 ing profusion with which spicules are secreted Ijy developing 

 Spongillids from water in which the percentage of silica present 

 must have been exceedingly small. The young sponges climbed 



1 Mtm. Ac. St. Felersb. (7) xxvi. 1878, p. 10. 

 - Sollas, Challenger Rex>ort, xxv. yi. Ixiii. p. Ixxxviii. 



I 



