118 JOURNAL OF THE L^ay, 



plant-like objects which resemble bunches of compact sea-weed 

 more than anything else. It would be difificult for the unin- 

 structed to recognize them as sponges : yet such they are. If 

 we take one of the simplest of these, we find that it is shaped 

 somewhat like a vase. By its base it was attached to its anchor- 

 age. At the upper end is an opening, the osculum, leading into 

 a central cavity, the ventriculus.. The wall is (usually) of two 

 layers. The inner consists of cells provided with long cilia, the 

 outer with cells furnished with spicules The wall may be con- 

 tinuous, or it may be perforated with one or more pores through 

 which water passes from without into the ventriculus. If the 

 wall be thick, the pores will be many, and will represent as many 

 canals leading to the central cavity. When these pores are so 

 numerous as to lie close together, the ciliated cells are no longer 

 observed on the wall of the main cavity, but will be found lining 

 the canals. These cells, when sufficiently magnified, are seen to 

 have a body-portion to which is attached the cilium, while 

 around the base of the cilium and extending out from the body 

 of the cell is a hyaline collar which gives to the whole a bottle- 

 shaped appearance. The cell-body usually contains a nucleus, 

 a nucleolus, and a contractile vacuole. These cells are the feed- 

 ing organs of the sponge ; and the cilia, by their motion, cause 

 currents in the water and thus procure for the cells their food. 

 Such food-particles as cannot be absorbed and appropriated are 

 sent on with the general current into the ventriculus, from which 

 they are expelled at the osculum. 



The resemblance of these flagellate collared cells to monads, 

 combined with the supposition that the sponge consists exclu- 

 sively of communities of such cells, has caused this animal 

 to be ranked as a Protozoon. But the study of the egg and its 

 development leads me to a different view. The investigator will 

 notice in the wall of the sponge, not only flagellate collar-bear- 

 ing cells, such as have been described, but also, behind these, 

 other cells of various kinds which are unciliated, and are some- 

 times seen grouped in small clusters. Some of these inter-tissue 

 cells, situated just beneath the lining of a canal-wall, assume 

 special functions ; and by self-division each original cell becomes 

 transformed into a little group of cells, some of which are large 

 and some small. The smaller are ciliated and the larger not. 

 The segmentation continues until an embryo is formed in which 



