Mr Macvicar on the Seed of the Stipa Pennata. 343 



brown. The fracture is conclioidal, without any trace of clea- 

 vage. The surface of the crystal is shining and smooth, but 

 the fracture surface splendent ; and lustre between vitreous and 

 resinous. Its constituent parts are as follows : Titanic acid 

 62.75y hme 12.85, oxide of uranium 5.18, oxide of cerium 6.80, 

 oxide of manganese S.75, oxide of iron ^.16, oxide of zinc 0.61, 

 water 4.20, fluoric acid, quantity not determined, magnesia a 

 trace, = 97.30. 



The Lam of the Preservation of Species, illustrated hy the Phe- 

 nomena of the Seed of the Stipa pennata. By Mr John Mac- 

 vicar, Lecturer on Natural History in St Andrew's. (With 

 a Plate.) Communicated by the Author. 



XJLLTHOUGH it caunot be said that the primary object of nature, 

 in reference to a species, is to prevent its destruction, yet its ex- 

 istence is an essential condition to that end, whatever it may be, 

 and accordingly, nowhere do we observe a more admirable me- 

 chanism, than in those organs which are most eminently conserva- 

 tive or reproductive. The general law by which their develope- 

 ment and efficiency are regulated, may perhaps be thus stated, 

 that, in proportion as the causes operating to destroy a species 

 increase, so also do the organs or functimis operating to pre- 

 serve it. 



Thus, as we descend the scale of animated beings, the succes- 

 sive species become more and more restricted in their faculties, 

 their cunning, or swiftness, or force, by which they may meet 

 their enemies, the number of which is also increased, or 

 in those resources by which they may survive the violent 

 action of the elements, which beat upon their more minute 

 and simple structures, as rudely, and as boisterously, as upon 

 the more perfect animals. Their liability to destruction, then, 

 becomes greater as we descend. But to counterbalance this, 

 we find that, in obedience to the law which has been stated, the 

 very degradation of their structures becomes subservient to their 

 existence. For, by a collateral diminution of sympathies, the 

 life of the individual becomes more independent of partial in- 



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