324 Proceedings of the 



He concluded the lecture with remarking, that since the dis- 

 covery of the placental nerves proves the existence of a communi- 

 cation through their medium between the brain of the child and 

 that of the mother, some light may be thrown upon the degree of 

 dependance in which the foetus is kept, during the whole time of 

 utero-gestation, and upon the influence of the bodily and mental 

 affections of the mother upon the child ; in further illustration of 

 which, several instances were detailed in proof of the descent of 

 various peculiarities of the mother to the offspring. 



Another paper was also communicated by Sir Everard Home, 

 entitled Observations on the Changes the Ovum of the Frog m71- 

 dergoes during the formation of the Tadpole. 



The ova of the frog when in the ovaria, consist of dark vesicles, 

 which acquire a gelatinous covering on entering the oviduct, and are 

 completely formed by the time they reach the cavities in which 

 the oviducts terminate, and during their expulsion from which 

 they receive the male influence ; after this the contents of the 

 ovum, previously fluid, coagulate and expand, the central part 

 being converted into brain and spinal marrow, while in the darker 

 substance of the egg, the heart, and other viscera are formed. 



The membrane forming the vesicles, being destined to contain 

 the embryo when it has become a tadpole, enlarges as the embryo 

 increases, and may be said to perform the office both of the shell 

 and its lining membrane in the pullet's egg, serving as defence, and 

 allowing of aeration. 



The black matter which lines the vesicles, probably tends to 

 the defence of the young animals from the too powerful influence 

 of the solar rays, frog-spawn being generally deposited in exposed 

 situations. Sir Everard observed, that in the aquatic salamander, 

 an animal whose mode of breeding closely resembles that of the 

 frog, this nigrum pigmentum is wanting, but that that animal 

 deposits its eggs within the twisted leaves of water-plants which 

 afford them d-n equivalent protection. 



