GEMMULES OF EPHYDATIA 



177 



Ephydatia Jiuviatilis uormally produces not only free-swim- 

 ming larvae of sexual origin, but also internal gemmules arising 

 asexually. Tliese bodies appear in autumn, distributed through- 

 out the sponge, often more densely in the deeper layers, and they 

 come into activity only after the death of the parent, an event 

 which happens in this climate at the approach of winter. 



Weltner ^ has sliown that on tlie death and disintegration of 

 the mother sponge some of the gemmules remain attached to the 

 old skeleton, some sink and some float. Tliose which remain 



Fig. 71. — Portion of the skeletal franie- 

 work of E. fluviatilis. a. Main 

 fibres ; h, counectiug fibres. (After 

 ^Veltner.) 





Fig. 72. — Spicules of JiJ. Jiuviatilis. a.h.c^ 

 Oxeas, spined and smooth ; d.e, aniphi- 

 discs, side and end views. (After 

 Potts.) 



attaclied are well known to reclothe the dead fibres with living 

 tissue. They inlierit, as it were, the advantages of po.sitiou 

 which contributed to tlie survival of the parent, as one of th& 

 selected fittest. The gemmules which sink are doubtless rolled 

 short distances along tlie bottom, while those which float 

 have the opportunity of widely distributing tlie species witli 

 the risk of being washed out to sea. But even these floating- 

 gemmules are exposed to far less dangers than the delicate free- 

 swimming larvae, for their soft parts are protected from shocks- 

 by a thick coat armed with amphidiscs. 



The gemmules are likewise remarkal)le for their powers of 



' Arch. Xalurij. li.\. 1890, p. "240. 

 VOL, I X 



