T H E F R O G. 169 



The common Brown Frog couples early, generally about the middle 

 of March. The male is ufually greyifh brown -, the female inclining to 

 yellow, fppckled with brown. At this time their colours are nearly alike 

 on the back; but as they change their fkins almoft every eighth day 

 (the old one, after falling off, affuming the form of mucus), the male 

 grows yellower, and the female browner. In the males the arms and 

 legs are mucTi the ftrongeft ; at this time thev have on their thumbs a 

 kind of fiefhy excrefcence, which they fix firmly to the bread of the 

 female. Couple once a year: continue united days together. Their 

 bellies greatly fwoUen ; the female with eggs, tlic male with a limpid 

 water. He throws his fore legs round her bread, and clafps his fingers be- 

 tween each other ; the thumbs prefiing with their thickeft fides againft 

 her bread ; nothing can induce him to let go his hold : the grafp 

 feems involuntary and convulfive ; they fwim and creep together till the 

 female has died her eggs ; thefe form a kind of cord, united by a gluti- 

 nous matter which covers them : thefe the male impregnates as they are 

 ejefted. 



A fingle female produces from fix to eleven hundred eggs ; in general 

 by a fingle effbrt, though fomerimes die is an hour in this tadc. 

 While thus engaged, the male promotes their expulfion by working 

 with his thumbs, and compredmg her body clofcly. The eggs, when 

 excluded, expand into a round form, and drop to the bottom of the 

 water. 



The egg, or little globe, black on one fide, whitidi on the other, 

 ■which produces a tadpole, is furrounded with two different kinds of 

 liquor, each inclofed in its proper m.embrane. That which immediately 

 furrounds the globe is clear and tranfparent ; that which furrounds 

 the whole is muddy and mucous. The tranfparent liquor ferves for 

 nouridiment to the tadpole from timiC to time, anfwering the fame pur- 

 pofes as the white of the egg to birds. The tadpoles, when this mem- 

 brane is broken, are found to adhere to it by their umbilical cord, which is 

 attached to the head. 



At the bottom of the water the white quickly and fenfibly increafes. 

 After four hours the eggs begin to enlarge; and, growing lighter, mount 

 to the furface of the water. After eight hours the white grows thicker, 

 the eggs lofe their blacknefs, and, as they increafe in fize, fomewhat of 

 their fpherical form. After fifteen days the eyes appear (fometimes fnut), 

 and the lineaments of the hind legs. As the fcetus increafes in fize, the 

 &in lengthens : where the toes will be, is marked by little knobs j and 



F f 2 though 



