271 



steps by steps, until it had attained the degree of complexity 

 which we see at the present day/^* 



This clear statement of the proposition amounts to an 

 assertion that all the differences between life-forms, ancient 

 and modern, have arisen from time to time by virtue of 

 " inherent properties/^ 



The eloquent lecturer then sets himself to prove that this 

 hypothesis coincides with the actual life-history on the globe. 

 The evidence on which he relies is, that of the animal inhabiting 

 the shell of the pearly nautilus, as compared with the indica- 

 tions presented by fossil shells of the same general kind. 

 He selects from among the ancient fossils, one called an 

 orthoceratite, a perfectly straight form; he takes this and 

 claims for it the distinction of having been the father and 

 founder of the whole nautiloid tribe. He says that it first 

 underwent a slight curvature and became the cyrtoceras; in 

 course of time the curving and rolling up of successive individuals 

 became gradually more and more complete, until it finally 

 issued in the beautiful Nautilus Fompilius of the present seas. 

 That the proposition may be more fully before you, I quote 

 further from the report: — " Unquestionably, nautili were found 

 as far back as the Upper Silurian age. Before that time there 

 were no nautili, but there were shells of the orthoceratidte — 

 of which there were magnificent examples before him — which 

 resembled those of the nautili in that they were chambered, 

 siphoned, &c., with the last chamber of such a size that it 

 obviously sheltered the body of the animal. He thought no 

 one could doubt that the creatures which fabricated these still 

 earlier shells were substantially similar to the nautili, although 

 their shells were straight, just as a nautilus shell would be if 

 it were pulled out from a helix into a cone. Then came the 

 forms known as cyrtoceras, which were slightly curved. Along 

 with these they had the other forms which were on the table, 

 and in which the shell began to grow spiral. The next that 

 came were forms of nautilus, which differed from the nautilus 

 of to-day in that the septa were like watch-glasses, and that 

 the whorls did not overlap one another. In the next series, 

 belonging to the later palaeozoic strata, the shell was closely 

 coiled and the septa began to be a little wavy, and the whorls 

 began to overlap one another. And this process was continued 

 in later forms, down to that of the present day. Looking 

 broadly at the main changes which the nautilus stock under- 

 went, changes parallel with those which were followed by the 



Rede Lecture, Nature, June 21, 1883, p. 189. 



