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PROF. ACJASSIZ'.S 



LECTURES ON EMBRYOLOGY. 



DELIVERED BEFORE THE LOWELL INSTITUTE 1848-9, 



LECTURE I. 



The time has past when it was possible to doubt 

 lhat there is order in Nature, when the existence 

 fcf a general system regulating the whole creation 

 could be questioned. However,, it has been oaly 

 step by step that man has acquired an insight into 

 this plan. Knowledge was to be gained before 

 this wonderful arrangement of nature could be 

 understood. And it was not at once fully under- 

 stood. Understanding has been acquired gradual- 

 ly, successively and With difficulties. However, 

 now we have sufficient data to be able to satisfy 

 ourselves that the various views which have been 

 brought forward respecting the order of nature 

 are not altogether fanciful, that they are not mere 

 artificial means to assist us in our investigations. 

 We can be satisfied that they correspond more or 

 less to nature. We have the positive hope that 

 they will one day correspond entirely to the nat- 

 ural phenomena, when we see how the investiga- 

 tions which are carried on in different directions 

 by different authors go on, converging gradually, 

 assisting each other, and harmonising subjects 

 which at first seamed entirely obscure, if not en- 

 tirely inaccessible. 



The first attempts to an illustration of therela c 

 tions which exist among the natural phenomena 

 which exist in particular in the animal kingdom- 

 were traced from external characters. It was 

 from external appearances that scientific men in 

 the beginning tried to combine animals,as it seem- 

 ed to them they resembledeach other most. 



But the simple investigation of these external 

 characters was not sufficient. Mistakes were 

 made under the impression that the right thing 

 had been found. Animals, for instance, like the 



whale, were placed among fishes ; though now it 

 is very well known that those animals have no re- 

 lation to each other do not even belong to the 

 same class. Crocodiles and turtles were placed 

 among the viviparous quadrupeds, because they 

 have four legs. Barnacles were placed among 

 shells among oysters snd clams because they 

 had a solid external covering ; and other similar 

 mistakes were made, which have been successive- 

 ly corrected. 



The corrections of these mistakes have been 

 made after a certain knowledge of the internal 

 tructure of animals had been obtained. And it 

 was found so satisfactory to derive information 

 from the investigation of their internal structure* 

 that soon comparative anatomy and the knowl- 

 edge of the internal structure of animals became 

 the real foundation of the classifications of the 

 animal kingdom. 



It was the result of the brilliant investigations 

 of Cuvier, to show that a natural arrangement of 

 the animal kingdom could be based upon the struc- 

 ture of the beings which were to be classified. It 

 was from such data that arrangements could be 

 produced, according to which all the kinds of ani- 

 mals Which were brought together were found to 

 agree in the most essential peculiarities, even 

 when they had ilot been previously investigated 

 anatomically. 



This is one of the promising results of those in- 

 vestigations of Cuvier which made internal struc 

 ture the foundation of the natural system. But 

 he found at the same time, that otherwise natural 

 groups had the same structure ; and that from a 

 knowledge of a few individuals, a great many 



