4 Mr, J. Hogg on the Horny Sponges. 



indeed, strongly resemble those of the membrane of the Spon- 

 gilla fluviatilis, which I have described at p. 386 of the *Lin- 

 noean Transactions,' vol. xviii., and the second, the fixed spo- 

 ridia ; — the actual existence of these bodies in any of our Bri- 

 tish sea sponges I have never yet been able to -witness, and 

 which I account for from my not having examined them in 

 their native localities at the proper season of the year. Al- 

 though previously figured in Donati's work and in the * Zoo- 

 logia Danica,' the fixed sporidia were first distinctly pointed 

 out by Dr. Ehrenberg, as having been seen by him in many 

 sponges of the Red Sea. 



The reticulated transparent membrane and the fixed spo- 

 ridia, then, fully confirm the general description of the Spong'uB 

 Marina which I gave at p. 400, ' Linn. Trans.,' vol. xviii., in 

 these words : — " The sea sponges are furnished with a skeleton 

 of fibres interlacing, crossing, and anastomosing with them- 

 selves ; generally also strengthened with those singularly 

 crystallized particles termed spicula ; with a parenchymatous 

 soft portion or jelly; with a fine and transparent enveloping 

 membrane ; with numerous minute pores ; and frequently 

 with larger orifices or oscules, which are more sparingly and 

 irregularly dispersed over their surfaces ; with passages or 

 canals communicating through the pores and oscules one with 

 another, along which the water finds a ready course or circu- 

 lation, and affords nutriment to all the inner parts of the 

 masses ; with locomotive sporules ; and in some species with 

 fixed sporidia." 



Mr. Bowerbank has however omitted to say whether these 

 sporidia were softish or hard, and whether the parenchyma- 

 tous portion or jelly was composed of minute globules or not; 

 nor has that author given us the names of the species which 

 he has described. Next, if we examine Mr. Bowerbank's 

 plate, we see the fixed sporidia well drawn at fig. 8 in their 

 natural position, but he has neglected to magnify any of them 

 separately. Fig. 7 gives a representation of the reticulated 

 transparent membrane, which, I believe, is quite new, and 

 has never yet been figured in any engraving of the sponges. 



Again, Air. Bowerbank in the abstract of his paper, which 

 was communicated to the Microscopic Society, and published 

 in No. 1 (for March last) of the ' Microscopic Journal,' men- 

 tions some of the horny sponges of commerce that were re- 

 ceived from the Mediterranean, in which spicula were like- 

 Avise discovered ; but the vascular tissue surrounding the fibres 

 there described, I am strongly inclined to agree with Dr. 

 George Johnston in thinking " as of no more than specific 

 importance." 



