24 MICROSCOPICAL OBJECTS FOUND 



of many of the Eolidse,* constitute important 

 links connecting them with the animal kingdom. 

 By what mysterious process the simple textures 

 of the sponges have the power of throwing into 

 such exquisitely beautiful forms the silica obtained 

 from the waters of the ocean, it is impossible to 

 say. The manner in which each species pre- 

 serves its own, in many instances peculiar, 

 form, indicates that there is some apparatus for 

 effecting the object which has as yet escaped 

 detection. In a number of instances, a species 

 may be identified by its elaborately marked 

 spicula ; and in others, where one general type 

 prevails, as in the case of the acicular spiculum 

 amongst the Halichondrise, the different species 

 often present well marked peculiarities of size and 

 form. Sponge spicula are not equally numerous 

 in all the specimens of Levant sediment that I 

 have examined. In some they are very abundant 

 — in others they are comparatively rare. This 

 was to be expected, as any local causes influencing 

 the growth of living sponges would also affect the 

 distribution of their spicula. 



The most common form is the calcareous tri- 



* See Alder and Hancock's Monograph on the British 

 Nudibranchiate MoUusca. • 



