84 MANUAL OF ZOOLOGY. 



in much greater numbers, are greatly smaller in size, and are 

 termed "pores," or "inhalant apertures" (fig. 23). Both the 

 oscula and pores can be closecfat the will of the animal; but 



A B 



Fig. 23. A, Axinclla polypoides, a fibrous Sponge showing oscula and pores; B, 

 Sycandra ciliata, a calcareous Sponge, showing the single terminal osculum. (After 

 Schmidt.) 



the oscula are permanent apertures, whereas the pores are not 

 constant, but can be formed afresh in the outer protoplasmic 

 covering, whenever and wherever required. The " sponge- 

 flesh," which invests the entire skeleton, is found upon a 

 microscopical examination to be composed of an aggregation 

 of rounded protoplasmic bodies the so-called "sponge-par- 

 ticles" or "sarcoids" (fig. 24). Some of thesejire provided 

 with a singleflagellum, surrounded by a membranous collar 

 (fig. 24, B) jwHile others are capable of emitting pseudopodia 

 from all parts of their surface (fig. 24, C). The former of these 

 resemble Flagellate Infusoria, and the latter are similar to 

 Amoeba; and both possess a nucleus and contractile vesicle. 

 Others of the sarcoids, again, become undistinguishably amal- 

 gamated with one another in progress of growth, and thus give 



