170 



PRINCIPLES OF ANIMAL BIOLOGY 



the mesoglcea (gelatinous material) of the sponge. These cells are 

 enclosed within a dense layer of material in which spicules of peculiar 

 types may be imbedded. Gemmules are usually produced in abundance 



Fig. 127. — Gemmule of the freshwater sponge Ephydatia, in schematic cross-section. 

 1, cells; 2, chitinous case; 3, shell with amphidisc spicules; 4, foraminal aperture. {From 

 Hesse and Doflein.) 



during summer and fall. When the body of the sponge disintegrates 

 the gemmules (Fig. 127) are left clinging to the log or stone to which the 

 sponge was attached. They may remain here or they may be transported 



Fig. 128. — Origin of sponge by asexual repro- 

 duction. A, young freshwater sponge recently 

 emerged from a gemmule; B, outline sketch of 

 the gemmule of the same species; fa, foraminal 

 aperture; os, osculum; sp, spicule. The scale 

 beside the figures indicates their size. 



Fig. 129. — Statoblasts of Cristaiella 

 rnucedo. a, surface view; b, side view. 

 (From Scdgu'ick, after Alhnan. Cour- 

 tesy of Macmillan Co.) 



considerable distances by water currents or perhaps on the feet or beaks 

 of water birds. With the return of favorable conditions the bud en- 

 closed within the outer coating of the gemmule begins to develop. In 

 some manner it removes the plug which closes the aperture of the covering 



