OF THE COMMON FROG. 



459 



upon it, never quitting it for some days, during 

 which their size is considerably augmented. 



In the course of my observations on these ani- 

 mals, having occasion, a few days after their exclu- 

 sion, to remove a mass of the gelatinous matter 

 in which they had been contained, from one vessel 

 to another, I was surprised at perceiving that the 

 tadpole still adhered to it, at the same time ap- 

 pearing to make frequent struggles to effect its 

 liberty, and in which, in the course of a short time, 

 it succeeded. On examining another, under like 

 circumstances, with the assistance of a lens, I per- 

 ceived that this was caused by a transparent fila- 

 ment or cord, proceeding from the centre of the 

 globule, and attached to the belly or under-side of 

 the animal. 



The idea of the umbilical cord, by means of which 

 the foetuses of mammiferous animals are nourished 

 in the placenta of the mother, immediately occurred 

 to me, and I was curious to know, whether, in the 

 case of the tadpole, this apparently similar structure 

 might not be subservient to the same end. 



As this might be ascertained by cutting the 

 connecting cord immediately after the exclusion of 

 the tadpole from the centre of the gelatinous body, 

 and observing the rapidity or the slowness of its in- 

 crease, compared with the growth of such as remain 

 attached to it, I resolved to institute a course of ex- 

 periments to that effect. In consequence, however, 

 of one of those unfortunate mishaps which occasion- 



