OBSERVATIONS ON INCUBATION. 347 



2. Of sixteen duck's eggs put under two hens in May, all but four were hatched. 

 Of these four, two were found to contain each a foetus well advanced. In the 

 other two there were no traces of development. Of one of these the white and 

 yolk were distinct, and little altered ; of the other the white and yolk were com- 

 mingled, very liquid, and had a slight disagreeable smell. It is worthy of remark, 

 that there was a thick layer of mucor (M. mucedo) on the air vesicle of each of the 

 eggs containing a foetus ; it was nearly black ; in a less degree it was found on 

 the lining membrane of the shell of all three. Air from one of these eggs, equal 

 in volume to "67 cubic inch, consisted of about 20 oxygen and 80 of azote. 



3. Ten eggs were put under a hen on the 24th of February. Three only were 

 hatched. The seven unproductive eggs swam in water. In the first examined 

 a foetus was found well advanced ; the fluid brownish and offensive. In the 

 second the yolk and white were mixed, of a yellow colour, curdly, and offensive. 

 In the third the contents were similar, but only slightly offensive. In the fourth 

 they were more liquid, not curdly, very slightly offensive. In the fifth the yolk and 

 white were only partially mixed, of a bright yellow, and not offensive. In the 

 sixth there was a foetus about one quarter the size of that of the first ; the yolk 

 and white mixed, of a dirty yellow, and offensive. In the seventh there was also 

 a foetus ; it was less advanced than that of the first, but more than that of the 

 last ; the yolk was brownish-yellow, the white gelatinous and transparent ; both 

 offensive. 



VI. Conclusions. 



What are the conclusions to be drawn from the foregoing results? The 

 changes experienced in the egg, as described in the several experiments, are so 

 many and various, and the difficulty of referring them to their causes is so great, 

 that I have much hesitation in drawing any decided inferences from them, espe- 

 cially as regards suspension of vital action, in the trials, whether with the air- 

 pump, lime water, or ice-house, in which incubation was afterwards successful. 



In the various experiments, it may be said that the whole of the oxygen was 

 not withdrawn from the eggs, that a minute portion remained sufficient to main- 

 tain a very low degree of vitality, enough, at least, to place in equilibrium for a 

 time the antagonistic agencies — those administering to life and death. I shall 

 relate one experiment which seems favourable to this view. On the 13th of May 

 three newly laid eggs were put into water sufficient to cover them, and, with a 

 piece of phosphorus placed by the side of the containing vessel, were subjected to 

 the air- pump until the 28th. After the greater portion of the air had been ex- 

 tracted from the water and the eggs, the phosphorus ceased to shine until the 

 instant that the pump was worked (it was worked twice or thrice daily, and was 

 in good order) ; then there proceeded from it flashes of light, lighting up the 

 interior of the bell-glass, suggestive of its vapour being diffused through the 



