193 Mr. J. Hogg on Dr. Nardo's Classification of the Spongiae. 



Wishing to re]jeat some of my former experiments on the 

 Spongilla jiuviatilis, I this summer procured a fine piece grow- 

 ing upon a brick, and kept it in fresh water from July 13 to 

 July 25. Obtaining from it many of the locomotive sporules, I 

 placed some of them whilst they were fresh and in full activity 

 in a little water under the highest power of my microscope ; but 

 I could not say positively that their motions were effected by 

 means of cilia. I now, however, strongly lean to that opinion ; 

 for I fancied that I could at times, in a strong light, discern 

 some ciha. My microscope is an old one (by Jones), and not 

 having sufficient magnifying power I could not satisfy myself of 

 the presence of cilia : indeed the sporules themselves are so small 

 and delicate that they require much skill in observing, a great 

 light and a powerful microscope to enlarge sufficiently such ex- 

 ceedingly minute organs as cilia, and especially when continuing 

 in rapid motion. So also, the existence of the same organs in 

 other parts of the sponges may probably hereafter be ascertained 

 by the assistance of a microscope of a recent and improved con- 

 struction. 



I have lately been enabled to witness through the microscope 

 the curiously formed spicula much resembling cotton-reels, which 

 were taken from the spicular crust of the sporidium or seed-like 

 body of our freshwater sponge. See Mr. Carter's PI. III. fig. 6/ 

 and d, August Number 1849, ' Ann. and Mag. Nat. Hist.' 



On again submitting this summer a living mass of the Spon- 

 gilla, placed in fresh water, to the direct and full influence of the 

 sun, I found the same results, which I have before detailed, to 

 occur with regard to the development of the green colour. The 

 same mass, which, as far as I could perceive, was entirely devoid 

 of any Confervee, or other minute plants growing upon it, like- 

 wise gave out in the sun's rays numerous bubbles of gas : many 

 of these I collected with care and put them into a little phial ; I 

 then inserted a small lighted taper, which I observed to burn with 

 increased clearness and beauty when it came in contact with the 

 gas derived from those bubbles within the phial; thus showing, 

 as it appeared to me, that the gas so evolved was oxygen. 



I may, moreover, mention that the same Spongilla was inha- 

 bited by a great many of the remarkable green sponge-insects 

 which have been previously described by ]Mr.>\'estwood, and which 

 I have usually noticed as accompanying that living substance. 



Communications have not long ago been made relative to the 

 powers of " certain sponges " in excavating holes in the valves of 

 shells, which are highly interesting ; yet they appear to me to 

 require much further investigation. Can these holes and perfo- 

 rations be chiefly caused by the "sponges," or rather CUoike 

 secreting or giving out a strong acid, which, acting on the lime 



