236 Scientific Notices — Miscellaneous, [Sept. 



titute of any umbilicus, and are only attached to the mother by 

 means of the mouth. 



Geoffroy St. Hilaire has lately discovered in some specimens 

 of the foeti of Didelphh Virginiana preserved in spirits, which 

 had been taken from the mother by Dr. Barton very soon after 

 their introduction into the pouch, evident vestii^es of placentral 

 organisation, and of an umbilicus. They were only five lines 

 long, and already formed ; in the two male which he examined 

 the umbilicus was large for the size of the animal, as it was also 

 in the female, and very distinct from the entrance of the pouch. 



Mr. Geoffroy observes, that the series of transformations com- 

 mon to all mammalia are Ovulum, Emhri/Oj and foetus. These 

 three stages of genital products require three distindt situations 

 which in the other mammalia are found in the sexual canal, but in 

 the Marsupialia they are very differently distributed throui;h in 

 aa equally continuous series. The ovulum and the embryo are 

 formed and developed in the sexual canal and the foetus out of it. 

 The womb is the third station in the mammalia, where the com- 

 mon foetus is incubated and nourished ; and the Marsupium or 

 nursing pouch is for the same purpose in the marsupial animals. 

 The difference, therefore, consists only in the name of the last 

 part, — (Ann. Sci. Nat. and Zool. Jour. i. 403.) 



Miscellaneous. 

 10. A Method of fixing Crayon Colours, By James Smithson, Esq. 



(To the Editors of the Annals of Philosophy.) 

 GENTLEMEN, London^ Jug. ^3, 1825, 



Wishing to transport a crayon portrait to a distance for the 

 sake of the likeness, but without the frame and glass, which 

 were bulky and heavy, I applied to a man from whom I expected 

 information for a method of fixing the colours. He had heard 

 of milk being spread with a brush over them, but I really did 

 not conceive this process of sufficient promise to be disposed to 

 make trial of it. 



I had myself read of fixing crayon colours by sprinkling solu- 

 tion of isinglass from a brush upon them, but to this too, I ap- 

 prehended the objections of tediousness, of dirty operation, and 

 perhaps of incomplete result. 



On thinking on the subject, the first idea which presented 

 itself to me was that of gum- water applied to the back of the 

 picture ; but as it was drawn on sized blue paper pasted on can- 

 vass, there seemed little prospect of this fluid penetrating. But 

 an oil would do so, and a drying one would accomplish my 

 object. I apphed drying oil diluted with spirit of turpentine; 

 after a day or two when this was grown dry, I spread a coat of 

 the mixture over the front of the picture, and my crayon draw- 

 ing became an oil painting. 



