380 Mr. Hogg's Observations on the Spongilla fluviatilis, 



Here, then, it will be apparent to every one how completely analogous the 

 locomotive germlike bodies of certain kinds of Sea Sponge are to those of the 

 River Sponge, and to the moving sporules of the club-shaped Ectosperma, 

 but with this exception, viz. that the first bodies are said to be endowed with 

 vibratory cilia. Nevertheless, I much desire that these bodies of the different 

 Marine Sponges, of which only a few species have been described by Pro- 

 fessor Grant, were again subjected to a more thorough and careful investiga- 

 tion, in order to establish with greater certainty the presence and nature of 

 their supposed cilia or cilialike appendages. Because, until a more intense 

 power of the microscope be brought to the examination of these bodies than I 

 can learn from the papers already referred to in the Edinburgh Philosophical 

 Journal*, to have been at that time used, I cannot hold it to be by any means 

 decided whether those currents there detailed be caused by real cilia or not. 

 And I am bound to state this as my opinion, yet with all due respect and 

 deference to the able observations of Professor Grant, inasmuch as I have 

 myself been nearly misled in regarding the currents issuing from the sides of 

 the locomotive sporules of the River Sponge, as being the vibrations of tufts 

 of cilia, as 1 have before mentioned, in consequence of using a microscope 

 made about thirty years ago, and one of an inferior power ; and had I not 

 been so fortunate as to have just had the opportunity of resubmitting some of 

 those same bodies to a more modern instrument of a considerably higher 

 power, I should uncjuestionably have declared that those sporules were fur- 

 nished with true cilia, and that the currents noticed by me were produced by 

 the vibratory motions of such cilia: whereas, in fact, their supposed cilia have 

 at length turned out to be merely pa])illa^. 



Wherefore, having thus escaped from an unavoidable error, I feel the neces- 

 sity of urging the re-examination of the locomotive germlike bodies of the Sea 



brane : these buds, when viewed in the microscope, were rather hollow in the centre, from whence 

 a shoot pushed forth." ïlie germination also of the sporules of the River Sponge as observed by me, 

 and described in a preceding page, is remarkably similar. 



* Dr. Grant appears to have used a magnifj'ing power of less than even 100 times in those re- 

 searches ; for he there writes, " I have used every effort in vain to detect them (polypi in the Sponge) 

 with a microscope magnifying nearly a hundred times." A'ide Edinb. New Phil. .lourn. for 1827, 

 p. 126. It is superfluous to comment on the great improvements that have been made in microscopes 

 within the last twelve years. 



