62 



MANUAL OF ZOOLOGY. 



sponge-particle is enabled to obtain nutriment; the process 

 being at the same time not improbably a rudimentary form of 

 respiration. 



Fig. 8. Diagrammatic section of Spongilla (after Huxley), a a Superficial layer or 

 "dermal membrane;" bb Inhalant apertures or "pores;" c c Ciliated cham- 

 bers; ^Anexhalant aperture or " osculum." The arrows indicate the direction 

 of the currents. 



The reproduction of sponges may be effected either 

 asexually or sexually, the following being a brief outline of 

 the phenomena which have been observed in the common 

 fresh-water sponge (Spongilla), in which the process has been 

 most accurately noticed. 



Fig. 9. a Gemmule of Spongilla', h Hilum; b Diagrammatic section of the gem- 

 mule, showing the outer layer of amphidiscs and the inner mass of cells ; c One 

 of the amphidiscs seen in profile ; d Fragment of the skeleton of a horny sponge 

 (after Bowerbank), showing the interlacing horny fibres with spicula. All much 

 magnified. 



In the first or asexual method of reproduction, which takes 

 place in the winter, the deeper portions of the sponge are 



