HALF AN HOUR WITH SPONGES. 



67 



ocujata. This has been called the " crumb-of-bread " 

 sponge (Halichondria panicea, Fig. 29), from its 

 resemblance, when dried, to a piece of the crumb of 

 white bread. When alive, however, its colour ranges 

 from light ash to yel- Fig. 29. 



low, orange, or green. 

 Its external shape 

 varies exceedingly. 

 Sometimes we find it 

 enveloping the stems 

 of larger seaweeds or 

 zoophytes, or encrust- 

 ing rocks or stones, as 

 in Fig. 29, where it 

 has done so in com- 

 pany with some sertu- 

 larians. Its surface is 

 quite smooth when the 

 sponge is alive, but 

 when dry it is minutely 

 reticulated. For some time after it is dead, if the 

 sponge masses are broken, it will be seen to be of a 

 yellowish-green internally. The membrane of this 

 species is exceedingly rich in spicules, and the entire 

 skeleton is made up of spicules cemented together, 

 as indeed is the rule with the other species of this 

 order. These spicules are long and spindle-shaped, 

 besides being a little curved (see Fig. 30). They 

 are pointed at each end. When sections of all these 

 sponges are mounted for the microscope, from the 



Halichondria panicea. 



