333 Mr. A. Hancock on the Excavating Powers of Sponges, 



ordinary currents, whicli setting in from the surface of the sponge 

 would convey the reduced matter into the principal channels, by 

 which it would soon find an exit through the eiferent papillary 

 apertures. I have before alluded to calcareous particles found 

 strewed along the channels inhabited by C. celata. These par- 

 ticles, measuring 2^0^^ ^^ ^'^ ^^^^^ lo^^o? ^^'^ apparently too large 

 to escape through the pores of the sponge, and are evidently not 

 the scourings of the excavation ; they are much too large to arise 

 in this way ; but are pieces probably cut out by a combination 

 of the minute drills just described. To understand how this 

 may be effected, we have only to svippose that numerous punc- 

 tures are made through a thin, slightly attached plate or lamina 

 of the oyster-shell, and that interspaces are left between the 

 punctures ; and it is clear that as the drilling goes on, many 

 of these interspaces will become detached in the form of de- 

 pressed, many-sided, angulatcd bodies. And such are those that 

 are found in the channels of the excavations. Those particles 

 of a similar nature occurring in the chambers in limestone are 

 undoubtedly produced much in the same manner. 



In the siliceous granules on the surface, and in the contractility 

 of these sponges, we thus find an explanation of their excavating 

 powers. 



We shall conclude this communication with the description of 

 a few of the species, premising that the figures of the spicula 

 represent them drawn to a scale, so that at a glance a pretty 

 correct idea may be obtained of their relative sizes. And it is as 

 well perhaps to observe, that in eveiy instance the full- developed 

 spiculum has been measured and figured. 



Cliona celata, Grant. PI. XIII. figs. 3 & 4. 

 C. celata. Grant, Edin. New Phil. Journ. vol. i. p. 78. 

 C. celata, Johnston, Br. Sponges, p. 125? 



Sponge of a clear yellow-ochre colour occasionally inclining to 

 olive, composed of a large open network of branches ; the meshes 

 irregularly angulated, frequently five- or six-sided, and occasion- 

 ally half an inch wide ; the branches stout, often y gths of an inch 

 thick, distinctly nodulous and generally depressed : papillse large, 

 some measuring yg^th of an inch in diameter*; for the most 

 part in a single row along the branches, but penetrating the 

 surface of the matrix without much apparent order, and placed 

 rather far apart from each other : terminal twigs rather short, 

 delicate, almost linear, and generally bifurcated. Spicula very 

 long, measuring upwards of jq^^ °^ ^^ vach in length, a little 



* In this and in the following descriptions the diameter of the papillae has 

 been determined by that of the papillary punctures. 



