CIVIC PKUBLE.MS KELATlXd TO .MOLLUSKS '2Hl 



It is quite possible tliat these liuiul»le creature.-, are doiug a work of 

 value many times greater than that represented hy their shells and 

 pearls, in the constant jiuritication of our lakes and streams. Exi»eri- 

 ineut has shown that a ^ood-siz.'d mussel filters ai»out four gallons 

 uf water thn>UL;h its .L;ilis jx-r hour, au<l since it hreatlM's and feeds 

 cuntiniu)usly, this means nraily 100 ,i;all(>ns daily y»'ar in and year out. 



Fig. 128. Fresh-water mussels, female, male, and side view, showin-; 



growtli lines 



Set up two ])erfectly clean ,:ilass aquaria exactly alike, put a iim-« 

 s«d in one of them, and note the difference in clearness of the water. 

 What may this mean in keeping reservoirs and }iark waters clear and 

 wholesome? 



Glochidia (£?/oc/j/s, " arrow point ") /-//; /n'storif. The eiigs <lev(do]. in 

 the gills of the parent muss(d into minute hivalves so uidike tin- adult 

 that they were long considered parasites. These are the <fln<fiii/iif and 

 when ripe they are extruded into the water. Here further developnn-nt 

 depends upon their attachment to gills, tins, or other parts of fishes. 

 A long byssus thread is present and probably helps in catching the fish, 

 and some species have the valves tipped with sharjvbarbed hooks, whiidi 

 catch into the skin of th(^ fish when they are snapped together. The 



