152 BRITISH SPONGES: 



through the surface, or beyond the margin of the ovum ; al- 

 t'iough the slight agitation of changing its water from time to 

 time, soon causes many of them, already formed within the 

 ovum, to project beyond its surface. This renders it probable 

 that all the spicula, even the naked groups, projecting round 

 the pores and orifices, were originally formed within the surface 

 of the soft matter. Analogy leaves no doubt, that these ova or 

 spherical portions of gelatinous matter, when ready to separate 

 from the parietes of the canals, are delivered by the currents 

 through the large fecal orifices as in the marine sponges ; 

 but I have not detected any cilia on their surface, nor seen them 

 swim about by their own spontaneous motions, like many ma- 

 rine ova, before fixing themselves. The ova were nourished 

 only with rain water, while the spicula were successively form- 

 ing in their interior ; which shows that these simple gelatinous 

 globules, in which neither vessel nor fibre are discernible, have 

 the power of secreting siliceous tubes from that pure element." 

 Grant. 



The Sphserulae are produced only under favourable circum- 

 stances. Although the Spongilla is not uncommon in the waters 

 of Berwickshire, yet a specimen with these bodies has never oc- 

 curred to us. Wlien they do exist they are usually in great 

 abundance, lying dispersed without order through the mass of 

 the sponge, and attached rather loosely to its fibres.* " I have 

 frequently," says Dr Grant, " found a portion of Spongilla 

 crowded with them, while another growing beside it contained 

 none ; and even the same portion sometimes presents them 



* " They are distributed very irregularly, but abound most in tlie 

 deeper parts, where they frequently lie loosely collected in groups of 

 about twenty or thirty ; they have no perceptible organic coiniection with 

 each other, or with the substance in which they are imbedded." Grant. 

 According to Link, each sporangium or spha>rula occupies a single cell, 

 to which it is exactly adjusted. Ann. dcs. Sc. Nat. Part. Bot. n. s. ii. 

 p. 328. 



