1823.] of the Egg during Incubation. Ill 



vascular;* it is, therefore, extremely difficult to conceive how 

 the earth in question can be introduced into the economy of the 

 chick from this source, particularly during the last week of 

 incubation, when a very large portion of the membranes are 

 actually separated from the shell. Secondly, both the albumen 

 and yelk contain, at the end of incubation, a considerable pro- 

 portion of earthy matter (the yelk apparently more than it did 

 originally) ; why is this not appropriated in preference to that 

 existing in the shell? In opposition to these arguments, it will 

 be doubtless stated, that the shell of the egg becomes brittle at 

 the end of incubation, and appears to undergo, during that pro- 

 cess, some other changes not at present understood. To which 

 it may be answered, that this brittleness has been attributed to 

 the separation of the membrana putaminis, and the exsiccation 

 of the parts by so long an exposure to the heat necessary to the 

 process of incubation ; and in this manner all the known changes 

 produced in the shell by incubation may, perhaps, be satisfacto- 

 rily accounted for. Until, therefore, it be demonstrated that 

 some other changes take place in the shell, I confess this argu- 

 ment does not seem to me to have much weight. I by no 

 means wish, however, to be understood to assert, that the earth 

 is not derived from the shell ; because, in this case, the only 

 alternative left me is to assert, that it is formed by transmutation 

 from other matter; an assertion, which I confess myself not bold 

 enough to make in the present state of our knowledge, however 

 strongly I may be inclined to believe that, within certain limits, 

 this power is to be ranked among the capabilities of the vital 

 energies." 



Dr. Prout has requested me to insert the following correction 

 of a passage in his paper : — In the twenty-second page of the 

 paper itself, or p. 398 of the Philosophical Transactions, line 6 

 from the bottom, for " after incubation," read " after it had 

 left the egg."— Edit. 



" " See an essay ' On the Connexion between the Vascular and Extra-vascular 

 Parts of Animals,' by Sir A. Carlisle. — (Thomson's Annals, vol. vi. p. 174)." 



