1864.] 641 



during indefinitely long periods of time from pre-existing species — 

 that the Great Author of Nature constructed his primordial Cosmos 

 in so perfect a manner, that ever thereafter it needed no interference 

 on his part — that it is not like the bungling machines put together by 

 human hands, which wear out in a few years and require constant at- 

 tention and supervision — but that, without any miraculous interposition 

 on the part of the Creator, the Creation has heretofore run, and will 

 continue hereafter to run its appointed course, one geological epoch 

 gradually succeeding to another, and one species gradually arising from 

 and supplanting another, till it shall seem fit to the Great First Cause 

 to destroy that work which, when he called it into being, " he saw to 

 be good," good not only for one brief geological era but for all time. 

 Rock Island, Illinois, Dec 14. 18G4 



POSTSCRIPT. 



Since my remarks on the '• Unity of Habits" in Insects were in print, 

 (pp. 567, 570, 574,) I have been much pleased to find that Professor 

 Agassiz recognizes the same great Law, with apparently the same limi- 

 tations, as regards animals generally, and extends it not only to the 

 genus, as I have done, but to the family. " The more I learn upon 

 this subject," he says, "the more am I struck with the similarity in the 

 very movements, the General Habits, and even the intonation of the 

 voices of animals, belonging to the same fimily." ( Esuat/ Chssif. p. 59.) 



It may be asked how I, who believe firmly in the Derivative Origin 

 of Species, can believe that it is impossible for species of the same genus 

 to have several heterogeneous and widely diiferent habits. " Your 

 Uniti/ of ffabits" it may be objected, " is irreconcileable with the 

 theory of the gradual development of existing species from pre-existing 

 species. If one species is derived from another, must not the new spe- 

 cies, while in an incipient state, diifer in its organization and often in 

 its habits from what may be called the mother-species? May not 

 the Gecidomi/ia that are said by Wagner to procreate in the larva 

 state, be simply a new genus in an incipient or nascent condition, that 

 will hereafter perhaps become developed into a whole family of insects 

 having the same peculiar and extraordinary habits?" I reply, in the 

 words of Linn;ieus, JSfatura non ag'd per salfnm. If Nature wished to 

 construct a race of insects, that should habituallv commence making new 



