not exceed 1^ cwt. per week ; but it is of very good quality, and is 

 used extensively in Italy under the name of Sal Inglese. 



Ore the Formation of Fat in the Intestine of the Tadpole, and on the 

 Use of the Yolk in the Formation of the Embryo in the Egg. By 

 Sir Everard Home, Bart. V.P.R.S. Read May 23, 1816. [Phil. 

 Trans. 1816,^. 301.] 



From the smallness of tadpoles in this country, they have not at- 

 tracted the notice of naturalists so much as their peculiarities deserve. 

 But those of the Rana paradoxa of Surinam being of a much larger 

 size, are fitter subjects for observation. The tadpole of this frog bears 

 so strong a resemblance to a fish, that it is commonly sold as such 

 for the use of the table. But as these are not to be had here in suf- 

 ficient quantity for examination, the author had recourse to the com- 

 mon tadpole of this country. 



This animal, as soon as it leaves the ovum, has ten filaments pro- 

 jecting from the neck on each side, which answer the purpose of gills. 

 In the young shark, while yet in the egg, there are twenty-four si- 

 milar filaments to answer the same purpose. In the common newt 

 also is a similar apparatus, but the number is only three on each 

 side. In each instance this structure is but temporary, and drops off 

 when the permanent structure of lungs in the frog, and of gills in 

 the shark, is completely formed. 



During the growth of the tadpole its abdomen becomes distended, 

 the intestine being then very capacious, and filled throughout its 

 whole extent with a soft substance, that burns with a vegetable 

 smell. Behind the intestine, along the posterior part of the abdomen, 

 is accumulated a quantity of fat of a yellow colour, inclosed in long 

 thin transparent membranous bags. During the conversion of the 

 tadpole into the frog by development of the legs, lungs, and other 

 organs before wanting, the whole of this fatty matter becomes ab- 

 sorbed, in the same manner as the yolk of the hen's egg is taken up 

 during the progressive growth of the young chicken. So that al- 

 though the egg of the frog differs from that of other animals of the 

 same class in having no yolk, a substance corresponding to it ap- 

 pears to be necessary previous to the formation of bones, and other 

 more solid parts of the perfect frog. For the production of this 

 matter, it is observed that the tadpole is provided with a most un- 

 common length of intestine, which contracts to one of ordinary size 

 as soon as the full supply of fat is generated. 



The author adds the result of various chemical experiments, made 

 by Mr. Hatchett and Mr. Brande on the spawn of the frog, from 

 which it appears, that it is of a nature between gelatin and albumen ; 

 that it contains no concrete oil like that of the hen's egg ; that the ova 

 of the lizard and snake, and of cartilaginous fishes, have, on the con- 

 trary, yolks which do contain a concrete oil, that in its nutritive quali- 

 ties corresponds to the butyraceous part of milk with which the young 

 of viviparous animals are supported for a certain time after birth. 

 VOL. n. E 



