On the Vhysiologij of the Egg. 305 



Albumina, with their proper membranes ; 3. The Chalaza ; 4. The 

 Follicnlus acris; 5. The Common Membranes; 6. The Exterior 

 Involucnim, 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The necessity of any description of these parts is superseded 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 Fabricics ab Aquapendente, Harvey, Malpighi, 

 and of many modern and enlightened physiologists ; I shall 

 confine myself, therefore, to Avhat I consider exclusively original. 



'J'he 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 onli/ purpose for which it is designed. No 

 Avhere 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/a'^«s 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 ir, 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 micrht 

 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 



