109 



Dr. Fordyce has proved by experiments, that all birds, 

 especially during the time of laying, require a certain quan- 

 tity of calcareous matter for the perfect formation of their 

 egg-shells. 



In opposition to this opinion, however, Dr. Paris, in 

 the I Oth vol. of Lin. Trans, says, "That a deficiency of 

 calcareous matter in the system is the cause of the absence 

 of the shell, no one will deny ; but that it depends on some 

 internal state, and not on the privation of lime, may be 

 shewn by the following circumstance. A hen, which I kept 

 for some experiments, had its leg broken in two parts. 

 The fracture was carefully bandaged ; three days subsequent 

 to which several eggs, destitute of shells, were formed on 

 the premises. The hen had deposited no perfect eggs, 

 nor were there any other birds from which those yolks 

 could have proceeded. I therefore conjectured that all the 

 calcareous matter designed for the formation of the shell 

 had been employed in the regeneration of the bone." 



Pigeons are particularly fond of carbonate of lime : this 

 instinctive partiality probably arises from their frequent in- 

 cubation. 



Vanquelin found the dung of the pigeon to contain a 

 peculiar acid, which is increased by the mixture of the 

 fceces with water. 



Birds having no urinary bladder, this fluid is received 

 into the rectum together with the fceces. The termination 

 of the gut is called cloaca, from this circumstance. Con- 

 nected with the rectum in moit species is a bag or purse, 

 called after its discoverer bursa fabricii, which secretes a 

 thick mucus : its structure is curious, and worthy of minute 

 examination. 



