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nels, but really made up of distinct cells, each having its own covering. 

 A little inquiry will show that the sarcode is the constant feature 

 whilst the skeleton may have its strength and figure given by siliceous 

 or calcareous spicules, or even by regularly disposed particles of sand- 

 It is found that water is absorbed by the smaller and more numerous 

 openings, and forced along in currents which are believed to depend 

 on the action of the cilia on some at least of the cells forming the 

 lining, which water as it passes affords both aeration and nutrition to 

 the cells, and is finally discharged through the larger openings called 

 oscula. It is found, also, that certain specialized cells produce the 

 reproductive elements, the matured ova being conveyed doM'n the chan- 

 nels through which also gemmules which have budded out on the sur- 

 face are carried forth to found new colonies. This is a general statement 

 of what is known of the life of sponges and is common to them all. 

 It will enable any one to understand the particulars which -we have 

 selected for notice. In the organization of sponges the spicula claim 

 especial attention, and although their various forms have been favour- 

 ite objects with the microscopist, the variety in their functions and 

 the relations in which the different kinds occur in the same species, 

 have chiefly become known through Dr. Bowerbank's labours. He 

 divides the spicula primarily into I. The essential skeleton spicula; 

 2. The auxiliary spicula. Of the former he speaks thus : — 



" In the siliceous sponges they are ususally simple, elongate in form, slight! j 

 curved, and occasionally more or less furnished with spines. They a"re either 

 irregularly matted together, collected in fasciculi, or dispersed within or upon the 

 keratose fibres of which the skeleton is to a great extent composed. Occasionally, 

 but not frequently, they assume the triradiate form. In the calcareous sponges, 

 beside the simple elongate form, the triradiate spicula are found in abundance. 



" All the elongate forms of spicula of the skeleton are subject to extreme variety 

 in length. In some species they maintain a great degree of imiformity, ■while in 

 others they vary to a very considerable extent according to the necessities arising 

 from the mode of the construction of the skeleton. When the areas of the reticu- 

 lations are large, they are generally long and rather stout, and are usually shorter 

 when the proportions of the network are small and close. When enclosed in 

 keratose fibre, they are most frequently smaller and shorter in their proportions 

 than those in the Halichondroid sponges. And in those species in which they are 

 dispersed over the membranous tissues, as in Ili/meniacidon, Bowerbaiik, they 

 are generally long, slender, and frequently flexuous. In the sponges of this struc- 

 ture having siliceous spicula the triradiate lorra of spiculum occurs but rarely, 

 while in the calcareous sponges, which consist of membranes and dispersed spicula, 

 the triradiate forms of skeleton spicula are the normal ones. 



" When the skeleton is constructed of large fasciculi of spicula, as in Telhea and 



