326 THE ZOOLOGIST. 



chambers, on the other hand, appear to be active elements which 

 perform an important function. 



The mode and process of nourishment in sponges is very 

 doubtful. Feeding experiments with carmine have shown that 

 not only the collared cells, as was previously believed, but 

 all the epithelial cells indiscriminately possess the power of 

 taking up fine particles. Infusoria, &c., liave been observed in 

 the amoeboid wandering cells in the interior of the body; 

 but nothing definite is yet known concerning the mode of 

 nourishment. It is quite certain that the sponge must extract 

 organic substances and oxygen out of the surrounding water 

 somehow, and that tlie epithelial cells, being the only elements 

 in contact with the water, must perform that function. It is 

 also evident that sponges cannot devour large animals, as the 

 extremely fine sieves which cover the inhalent pores, and the very 

 small pores which lead from the inhalent canals into the ciliated 

 chambers, make it impossible for large animals to enter the sponge. 



Even small Infusoria and Diatoms must encounter difficulties 

 before they can reach the ciliated chambers. Great precautions 

 are evidently taken to prevent all solid bodies from entering the 

 canal system, and particularly the ciliated chambers. It is further 

 quite clear that no nourishment can be taken up through the 

 oscula, through which the water is continually flowing out. 

 It seems to me most probable that the food of sponges is dis- 

 solved in the water, and that the sponge procures its nourishment 

 from the water in the same way that plants absorb their nourish- 

 ment from the solutions circulating in the soil. 



Now the question arises, which cells perform the function of 

 nutrition — tlie flat pavement epithelium of the canal- walls, or the 

 collared cells of tlie ciliated chambers. The collared cells seem, 

 from their situation and structure, best fitted for such a function. 

 But it must be considered that, although none of the higher 

 Coelenterates possess nephridia, yet the ciliated chambers 

 resemble kidneys so closely that it is not impossible they 

 really are such. They can hardly have to perform the combined 

 functions of segregating urea and of taking up nourishment. If 

 we consider the chambers as nephridia we must assume that 

 the flat, pavement-epithelium, and particularly the ectodermal 

 clothing of the inhalent canals, performs the function of taking up 

 nourishment. My own observations have brought me to this 



