THE PHYSIOLOGY OF THE SPOXGE. 



315 



3. FAC-SIMILE OF GRANT'S FIRST FIGURE. 



, Pores; e.oscule ; /, ova; f/. embryo entering cxrnrrenc cannls. Tho outward arrows show water 

 from osculcs ; the inward 0111-3 water entering I lie l>ores. 



feeding any kind of Sponge with carmine, killing it with osmic acid, hardening in alcohol, and then 

 cutting from it thin slioes for examination under a high power of the microscope. The flagellated 

 chambers will then be seen clearly marked out from the rest of the Sponge by the abundant presence 

 of the ingested colouring matter. So close a resemblance exists in all other respects between these 

 cells and certain flagellated infusoria, that in all probability they also feed in the same way, and we 

 may consequently de- 

 scribe the feeding of the 

 Sponge-cell after that 

 of the infusorian. The 

 flagellum, then, of each 

 Sponge-cell creates cur- 

 ivuts in the water to- 

 wards itself, and the 

 floating particles borne 

 along with these come 

 in contact with, and 

 adhere to, a delicate 

 film which surrounds 

 the long neck of the 

 cell like a collar (Fig. 5); 



the protoplasm of the collar is in a state of active circulation, streaming up one side and down 

 the other like an endless band ; the adherent food particles are thus carried by it to its base, 

 where they come in contact with the neck, sink into its substance, and find their way into the 

 basal part of the cell. A little drop of water is included with them, and thus the flagellated 

 cells not only eat but drink ; the food is next digested, and when all the goodness is got out of it, the 

 fiecal residue is extruded by an extemporised aperture from the cell, and forthwith carried out of the 

 Sponge by the outflowing currents. The circulation of the collar must expose a large and constantly 

 changing surface to the surrounding water, and so allow of the absorption of oxygen and the escape of 

 carl tonic acid ; this is one way in which the cell breathes. The proteinaceous compounds of the 



cell unite with oxygen, and in so doing liberate energy, which 

 is partly expended in maintaining the movements of the 

 flagellum and collar. The final products of the union of the 

 protoplasm with oxygen are water, carbonic acid, and urea 

 the second useless and therefore in the way, the last a deadly 

 poison; if the life of the cell is to be maintained, the carbonic 

 acid and urea, together with the excess of water, must be got 

 rid of or excreted. This is accomplished through the agency 

 of one or more contractile vesicles, which alternately expand 

 and contract, a slow expansion, during which water contain- 

 ing the other excreta accumulates in them, being followed by a 

 rapid contraction by which it is expelled. Thus the flagellated cells 

 eat, drink, breath, and excrete. They also grow and multiply 

 in number ; the excess of food which is not expended in 

 producing energy leads to increase in size or growth, and this, 



Fig:. 4. FLAGELLATED CHAMBERS (c) OF when it passes a limit, gives place to division or fission, by 



which the cells are multiplied : the division may be either longi- 

 tudinal or transverse ; in the first case it increases the number 

 of cells in the flagellated chamber ; in the second one of the 

 cells possesses an amoeba-like character, and wanders into the main tissue of the Sponge, to be 

 immediately described along with its other histological constituents. 



The Sponge, like all other Metazoa, is ultimately resolvable into cells ; and of these tissues are 

 built up, which are arranged in three definite layers the ectoderm, endoderm, and mesoderm. The 

 ectoderm is a layer of flattened polygonal cells (Fig. 6, ec), which cover the whole exterior of 



TURKEY BATH SPONGE IN CON- 

 NECTION WITH THE EXCURRENT (E) AND 



(After Schnl -.,:.) 



INCURRENT (l) CANALS. 



