PROPAGATION OF SPONGES. 33 



thin superficial canal in the vicinity of the closed 

 aperture, and established a new current, which con- 

 tinued even after the removal of the obstruction." 



Nothing is easier than the repetition of the above 

 interesting experiments. The entire surface of the 

 sponge is seen to be perforated by innumerable 

 pores and apertures, some exceedingly minute, open- 

 ing on every part of its periphery ; while others, of 

 larger dimensions, are placed at intervals, and gene- 

 rally elevated upon prominent parts of the mass. 

 Through the countless smaller orifices the surround- 

 ing water is continually sucked, as it were, into the 

 interior of the spongy mass, and it as constantly 

 flows out in continuous streams through the larger 

 openings. Organized particles that everywhere abound 

 in the water of the ocean are thus introduced on all 

 sides, and are doubtless employed as nutriment, whilst 

 the superfluous or effete matter is continually cast out 

 with the issuing streams as they rush through the 

 larger orifices. 



On examining a specimen of growing sponge during 

 the months of October and November, a remarkable 

 change may be observed to have taken place in its 

 internal texture. The parts which in summer were 

 transparent and nearly colourless, have now become 

 everywhere studded with opaque yellow spots, visible 

 to the naked eye (PI. I. fig. 1, a), and without any 

 definite form, size, or distribution, save that they are 

 most abundant in the deeper pa.rts of the sponge, and 

 are seldom observable at the surface. By examining 

 thin sections with the microscope at this period, it is 

 found that these bright yellow spots consist of groups 



c5 



