LECTURES ON EMBRYOLOGY. 



11 



further change of the same animal,when it loses its 

 gills entirely, and the posterior pair of legs assumes 

 an additional finger, the animal having four fingers 

 forward and five backwards. 



What changes does the frog have ? Hatched, he 

 is an animal without legs and without gills. [Plate 

 III. Fig. A] The salamander is hatched with 

 gills, but there is an epoch when it is without gills, 

 and without tail, and without head, and only a fis- 

 sure on the sides to indicate where the gills will be 

 formed, but not yet external gills. The frog has 

 not yet gills, and not yet a tail distinct from the 

 body. But next, the tail makes its appearance. 

 [Plate III. Fig. B,] when the head separates more 

 distinctly from the mass of the body, and the tail 

 grows longer, [Plate III, Fig. C] and here [Fig. D] 

 the tail grows still larger But in addition to that 

 we have a pair of anterior legs, and the gills have 

 disappeared. Then we have the same growth in 

 the posterior legs [Fig. E] coming out, though not 

 yet as large as they are here [Fig. F]. You see 

 that the size of the tail in proportion to the main 

 mass is reduced, and finally the tail disappears en- 

 tirely, and we have a frog, [Fig. G.j 



Here, in these facts we have not only the history 

 of the transformation of salamanders and frogs, 

 but we have a natural system of batrachians, and 

 there is no longer any arbitrary arrangement in 

 our system possible. Every thing is indicated in 

 the metamorphoses of the animals. 



Here we have a tailless, and gilless,and feetless 

 animal, [Plate III. Fig. A.] Suppose it grows no 

 longer it has the appearance of Csecilia. Next it 

 assumes gills rudimentary gills, in the condition 

 in which we see the primary growth, with rudi- 

 mentary legs formed. This stage corresponds to 

 Siren, [C]. And here is a second pair of legs formed, 

 [Plate III. Fig. E,] answering to Proteus, [AJ. And 

 here we have it shortened, [Fig. F.J the corres- 

 ponding animal in its iull formation. See Plate V. 

 Fig A. 



Whether or not this one [Plate VI, Fig. B]. will be 

 lower in the scale than this [Fig. C ] we have yet to 

 determine. And all these American species will 

 be examined, which will throw so much more ad- 

 ditional light upon this metamorphosis, that there 

 will be no doubt in regard to the position of that 

 animal. The two posterior legs have only four 

 fingers, while the other has five fingers. The tail 

 is shortened, as we see successively, in the frogs 

 and toads. But of the three toads, which is to be 

 placed higher and which lower ? That menobran- 

 chus stands lower than menopoma is plain, as in 

 the former the existence of the web is a mere rudi- 



mentary condition. The web fingers are observed in 

 all these early stages of growth, and those which 

 have distinct fingers, when fully grown, have them 

 webbed when young. Therefore, we shall see that 

 the frogs are not to be placed higher. And frogs 

 must be lowest, next treetoads and then toads the 

 highest, because their fingers are finally entirely 

 separated. 



And in conclusion, I will say, that in studying the 

 metamorphoses of animals, we may find in the 

 transformations -in the different formations 

 through which they pass, from the first formation 

 up to the full grown condition, a natural scale by 

 which we can measure and estimate the position 

 to ascribe to any animal belonging to this family. 



And, undoubtedly, the various genera of this 

 family which I have mentioned, will find their 

 places as soon as all the different metamorphoses 

 of these different animals are known. At present, 

 we know only the transformations of frogs and of 

 salamanders, through the researches of European 

 Naturalists. The metamorphoses of the numer- 

 ous species of that family which occurs in the 

 United States not having been investigated. 



But this agreement of transformation is most 

 remarkable. Nevertheless, we must acknowledge 

 that these perfect animals which occur in different 

 parts of the world in our day, are not copies from 

 metamorphoses from the different stages of the 

 growth of frogs ; but they are animals of a pecu- 

 liar kind, produced in various parts of the world, 

 showing proof that there is one and the same plan 

 ever producing the formation of this whole class, 

 as well in the developement of the young from the 

 beginning of their growth to their full grown stage, 

 as in the formation of the different animals which 

 inhabit different parts of the globe. 



There is a, freedom in the developement of this 

 plan, a freedom in which we can see the action of 

 the intelligent Author of all these things. 



We read here the intelligent action of the Creator 

 in the production of these animals ; and we read 

 more than the intelligent invention of his creation. 

 We read the omnipresence of his action, as his 

 action is developed on all parts of the globe, in the 

 United States, in Europe, in Japan, in South 

 America, and in all the portions of the globe. 

 And when developed in that way in its actual con 

 dition, we see that every one of them, when repro- 

 ducing its species, passes through these differen 

 changes the higher one, through more of the 

 changes ; the lower one, undergoing only the ear- 

 lier modifications. 



