OF THE NATURE OF SPONGES. 41 



stand in strong contrast with those of Lamarck. He has, 

 indeed, no doubts of their animahty, and assigns them a 

 position in liis system which gives them similar affinities 

 amongst zoophytes, but his own experience, as well as the 

 testimony of others, had convinced him that they were 

 truly apolypous. " I have often," says he, " watched 

 sponges at different times of the day and year, in the shade 

 and in the light, but never saw an appearance from which 

 the existence of polypes in them could be even conjectur- 

 ed." In regard of their alleged irritability, he appears to 

 have entertained doubts so far as the common mass of the 

 sponge is concerned, but he tells us that he had frequently 

 seen the oscula of species of his genus Manon * contract 

 themselves, so slowly and stealthily, however, that the fact 

 was rendered evident only by measuring their diameters 

 after an interval. " I never actually saw this motion, 

 but within 5 or 10 minutes separate oscula were noticed 

 to be wider or narrower at one time than they were before." 

 The sponges which he had an opportunity of examining 

 were divisible into three principal kinds, — one which is co- 

 vered on the minutely porous surface with a continuous 

 layer of gelatine through which the water filters into the 

 interior as it may be presumed to do in the agastric infu- 

 soria and gelatinous medusae, — another distinguished by 

 having distinct and ample oscula for the admission of the 

 nutrient water, — and the third are the tubular sponges 

 into whose cavity the water enters by the wide hole 

 which opens at their extremity. " The walls let in no 

 water, but it flows unhindered through the open end, and 



Manon — " Stirps lacunosa, e fibris reticulatis. Gelatina siiper- 

 ficiei ostiolis distinctis amplis. Polypi nulli." Handb. p. 4'22. 



