42 SPONGID^. 



probable, must for the present be considered as 

 un proven. 



In the interior of the canals of some marine 

 Sponges minute bud-like extensions of the sarcode 

 substance may readily be observed at certain sea- 

 sons of the year, and these, which are provided 

 with cilia, detach themselves from the body of the 

 parent, and probably, at length becoming fixed, 

 give rise to new Sponge formations. But it may 

 be questioned whether these bodies have not been, 

 in many cases, confounded mth true ciliated 

 swarm spores, similar to those which are found in 

 Spongilla. 



10. distribution The distribution of the 



Sponges may be compared, in many respects, to 

 that of the Fovaminifera. Like them they are 

 almost exclusively marine, are found in most 

 climates, but occur most abundantly, are more 

 varied in form, and luxuriant in growth, on the 

 shores of the warmer regions of the globe. Like 

 them also they have been found in most of the 

 geological epochs from the Silurian period to the 

 present. The Sponges of the chalk have more 

 especially attracted attention, the well known flint 

 nodules of that formation, in many cases, owing 

 their peculiar form to the presence of the extinct 

 remains of these animals. Several fossil Spongidse 

 have been figured and described of which PalcBO- 

 spongia is said to be peculiar to the Lower Silurian ; 

 Actinospongia, Goniosjjongia, and Perispongia 

 to the oolite ; and Hemispongia, Thalamospjon- 

 gia, Meandrospongia, Retispongia, Ccelopty- 

 climm, PleuTostoma, Turonia, with many others, 

 to the chalk. The curious genus Cliona, which 



