PROF. AGASS1Z S 



tal unity in all of them." This is a result which 

 is btjyond all doubt, which is beyond all contro- 

 versy. The eggs in the whole animal kingdom 

 are identical in structure. However, this funda- 

 mental unity must be restricted in one sense. 

 They are identical in structure for our senses, but 

 we cannot consider them as identical in a higher 

 point of view 4 as from each kind of egg there will 

 never arise but one kin of animal ; there is an 

 essential, though not a i. iiterial difference in the 

 egg from the beginning but in their material 

 structure the eggs of all animals are identical. 

 The first position must therefore be granted; but 

 with the restriction upon which I insist, that though 

 identical in structure, there is something which 

 presides over the individual growth, from the be- 

 ginning .even of the formation of the egg, and 

 makes each one give rise only to one sort of ani- 

 mals,, It could, then, just as well be said, that the 

 eggs, though apparently uniform, are essentially 

 different in different species. But Dr, Barry states 

 that the class, or the characters of the class, be* 

 come manifest in the egg in the germ, before the 

 order can be distinguished. That is to say, that 

 the first change which takes place in the embryo, 

 is to bring forth in the new animal what charac- 

 terises it as belonging to one particular class. 

 For instance, that a young rabbit would first as- 

 sume the peculiarities by which -it is referred to 

 the class of Mammalia t Next, the order becomes 

 manifest; but the family is not yet shov/n. The 

 young rabbit would be distinguished as belonging 

 to the gnawing animals* Next the family (here 

 the family of Hares) becomes manifest; but.the 

 genus not yet known. Next the genus (Lepus) 

 obvious; but not the species. Next the species, 

 (Rabbit) distinct; but the variety unpronounced. 

 Next the variety (white, grey, black rabbit) ob- 

 vious; but the sexual differences,scarcely apparent. 

 Next the sexual character obvious; but the indi- 

 vidual character not noticed. Next the individual 

 character developed in its most special form. This 

 is very logical, but not in accordance with nature 5 

 we may frame such a system in our closets, but it 

 does not answer our observations. 



Let us remember what we saw in the egg, with 

 which I began illustrating the growth of frogs* 

 Was it the character by which the frog is found 

 to belong to the class of reptiles, which was first 

 apparent ? By no means. .It appeared first, under 

 the form and with the structure of a fish, and not 

 under the form and with the characters of a reptile. 

 The lowest form of vertebrated animals was first 

 developed in the earlier changes of the egg, before 

 the class to which that animal belonged could be 

 recognized. Not only would the first form under 

 which the young Batrachian appears, exclude the 

 class 10 which it will belong afterwards, but even 

 the internal structure of the tadpole differs from 

 that of the reptiles They have no lungs, no inter- 

 nal saria! respiratory organ, nor even a rudiment 

 ?f it*, and also no nostrils communicating from 



outside with this innner hollow sac. What did we 

 find among the starfishes? among the echini? 

 Did we recognize there the hard plates or the 

 rows of regular plates which mark that class, of 

 the rows of suckers 1 By no means. Forms 

 which would lead us to mistake them for Polypi 

 or Medusa were first noticed, and not the indica- 

 tions of their class ; thus showing that there is no 

 such thing as an earlier development of those 

 characters which indicate the respective class of 

 the animals under observation in the progress of 

 embryonic growth. 



Next, it is said that the orders are manifest, but 

 not the genus. But let us take as a test the em- 

 bryo of a very well known animal among mam-= 

 malia. To what order does the cat belong? To 

 the Carnivora and to the family of Digitigrades. 

 What are now the characters of carnivora ? Sharp- 

 pointed, canine teeth, with chisel-like incisors and 

 various molars, the principal one of which is a 

 sharp-cutting tooth. The claws again, are strong, 

 curved nails, adapted for their peculiar mode of 

 seising their prey. Now, the young cat is already 

 far advanced in its development before it has any 

 teeth at all, and its paw is a real fm> with undivided 

 fingers, and without nails in the earlier stage of 

 growth. We have at first, therefore, not one of 

 those characters which distinguish the order of 

 Carnivora and the family of Digitigrades ; and 

 nevertheless such an imaginary order of succes = 

 sion in the development of parts is made the fun- 

 damental principle of a system which is given as 

 natural, though the whole is merely a logical par- 

 tition of principles. 



The genus next should be shown. What are the 

 characteristics of the genus, cats ? To have four 

 molars in the upper jaw, and three in the lower* 

 But before the cat has all its teeth, the genus can 

 be recognised, by its protractile and retractile 

 claws. The species indeed, is ascertained, is well 

 characterized, by its peculiar form, before we can re- 

 fer it to the genus, according to its soological char 

 acteristic. But it is said that the variety becomes 

 next obvious. The cat, however, may have already 

 assumed a peculiar variety of color 5 it may be a 

 grey or a white, it may be of any color before the 

 teeth, the characteristic of the genus, are fully de* 

 veloped. And as for its individual character, the 

 young kitten is playful, and shows its character 

 long before its peculiar genus is marked out; and 

 in short, every thing takes place in the reverse or 

 der from what it is supposed in this system. Nev- 

 ertheless, such views are considered as suited to 

 express the real gradation in the animal kingdom^ 

 from the simple reason that the whole statement 

 seems natural and logical. 



A renewed examination of the metamorphoses 

 of the frog will lead to the same conclusions. At 

 first we do not observe changes indicating the 

 class to which that animal belongs, but such char- 

 acters as would rather indicate the class of fishes ; 

 nor are the characters of the order of batrachians 



