BIVALVES. 43 
by a numerous and continually increasing progeny. 
The movements of this clumsy species, if such they 
may be termed, merely consist in turning from one 
side to the other, which they accomplish more by 
sagacity than by any natural agility or inherent 
strength. They contrive to bolster up one side by 
pushing against a deposition of soft mud, till they 
stand nearly upright; then, availing themselves of 
the flowing or ebbing of the tide, they open their 
shells, and are tumbled over by the pressure of the 
water. In this respect they differ materially from 
shell-fish in general. But 
“* Nature, all her children viewing, 
Equal, bounteous, cares for all.” 
To one she gives the faculty of locomotion; to 
another the means of safely remaining in its allotted 
station: and while the Solen, Donax, and Mytilus, 
frequently migrate to considerable distances from their 
usual places of abode, the stationary Ostrez firmly 
moor themselves to rocks and stones, by means of a 
bundle of small cords, denominated a byssus. 
These feeble creatures likewise possess the still 
more extraordinary faculty of profiting by the past. 
They are frequently taken from places covered by 
the sea, and placed in beds or reservoirs subject to the 
ebbing of the tide, and then, should they incautiously 
