336 



GENERAL BIOLOGY 



waters. Not all the sponges and bryozoans that live 

 in fresh waters are known to produce statoblasts, but the 



more common 

 shoal- water forms 



t^Hfe produce them in 



JJH very great abun- 



^^P dance (fig. 189). In 



early summer the 

 freshly grown 

 sponges may be 

 found by lifting 

 and overturning 

 boards, boughs, or 

 almost any solid 

 support that pro- 

 jects into the water, 

 and few if any 

 statoblasts will be 

 found; but in late 

 summer, when the 



sponge flesh is falling away, the statoblasts will be found 

 in patches scattered thickly over the surface as minute 

 rounded yellow bodies about the size of small mustard 

 seeds. These may be germinated after a resting spell, in 

 a watchglass, the numerous amoeboid cells contained in 

 them issuing separately from a side pore in the wall, and 

 then soon coming together to form a delicate chimney-like 

 tube, which is the first of the water channels of the new 

 sponge, and out of the summit of which the water can 

 very early be seen streaming. Doubtless it is in this 

 same way that new sponges are started in the sloughs 

 each spring. Many of them, doubtless, remain attached 

 to the support where they grew, there to develope a new 

 sponge on the old site. 



FIG. 189. Freshwater sponge (Spongilla fluviatilis", 

 disintegrating in late summer, showing the abun- 

 dant seed-like statoblasts. 



