G. GENERAL NATURAL HISTORY AND ZOOLOGY. 257 



probably covered with plates, as in some crocodiles, the head 

 itself being smooth. This fact has been ascertained in regard 

 to specimens of all the American genera, so that probably all 

 the species possessed it. D, Advance Sheet, April, 1872. 



NEW HADROSAURUS. 



The April number of the American Journal of Science con- 

 tains an account by Professor Marsh, the indefatigable pale- 

 ontologist, of his discovery of a new species of Hadrosaurus, 

 a giant lizard ; one of which, found in New Jersey, from its 

 enormous size, constitutes one of the chief attractions of the 

 Academy of Sciences of Philadelphia, where it is deposited. 

 The present animal is scarcely one third the size of the New 

 Jersey specimen. It was discovered near the Smoky Hill 

 River, in Western Kansas, and is named Hadrosaurus agilis. 

 4 D, April, 1872. 



METAMORPHOSES OF FROGS. 



Mr. Jourdain calls the attention of physiologists to the pe- 

 culiarities exhibited in the reproduction of various forms of 

 frogs, some of these having tadpoles of enormous size, much 

 larger than the adult which is developed from them, while 

 others, again, are scarcely larger in the tadpole condition 

 than afterward. The author compares the species having 

 the small tadpoles to insects with incomplete metamorpho- 

 sis ; these feeding and growing in a regular and gradual 

 manner throughout their entire life, up to the time that the 

 adult requires its normal and definite dimensions, growing 

 and becoming perfect gradually, like the hemiptera. The 

 case is different with the very large tadpoles. These, from 

 the period of their emergence from the egg^ grow very rapid- 

 ly, and quickly acquire a considerable size, like the caterpillar 

 of a butterfly, to which they may be compared during this 

 first period, which they make use of in acquiring an ample 

 nutritive reserve. In the second period they take little or 

 no food, but the substance stored is expended in building up 

 the new structure. Their volume diminishes, the animal liv- 

 ing and feeding by the absorption of its tail and the other 

 parts, which are taken up or lose their importance. This 

 period the author likens to the pupa condition of insects with 

 complete metamorphosis, the animal feeding upon substances 

 stored up by the larva. 6 B, May 27, 1872, 1417. 



