On the Physiology of the Egg. 305 
Albumina, with their proper membranes ; 3. The Chalaze; 4. The 
Folliculus: acris; 5. The Common Membranes; 6. The Exterior 
Involucrum, or Shell. 
The necessity of any description of these parts is superseded 
by the minute and valuable details which are to be found in the 
works of FABRICIUS AB AQUAPENDENTE, Harvey, MALPIGHI, 
and of many modern and enlightened physiologists; I shall 
confine myself, therefore, to what I consider exclusively original. 
The principal use of the albuminous portion of the egg is 
doubtless to afford materials for the growth, and nourishment for 
the support, of the ovular embryon: such however does not 
appear to be the only purpose for which it is designed. No 
where does Nature display more anxiety for the preservation of 
her offspring, or more wisdom to obtain her objects, than in her 
provisions to ensure an equable temperature to the fetus in ovo; 
a condition which is so essential to the evolution of the animal, 
that the smallest deviation overthrows the nice balance between 
the different actions that are to mature it, and produces fatal 
effects. "The albumen then I consider as a great defence against 
such an evil. The chalaza, by retaining the cicatricula at the 
source of heat, obviates the mischief that would accrue from | 
constant change of position; but the albumen, being a most 
feeble conductor of caloric, retards the escape of heat, prevents 
any sudden transition of temperature, and thus averts the fatal 
chills which the occasional migrations of the parent might | 
induce. As an illustration of the use and importance of such a 
structure, I may observe, that those fish which retain their vi- 
tality a considerable time after their removal from the water, as 
eels and tench, have the power of secreting a slimy and viscid 
fluid, with which they envelop their bodies. Is it not extremely 
probable that this matter, by acting like the albumen of the egg, 
and 
