MUSCA CARNARIA. 481 



same season might be too cold, and the winter coming on prevent 

 their hatching, I made the following experiment so as to spin out the 

 season for some time longer ; I put some eggs of silk- worms into a hot- 

 house at the following seasons : — 



Times when put in. Times when not hatched. 



11th August, 1775, were not hatched in April, 1776. 



20th September, 1775 „ in April, 1776. 



December, 1775 „ in April, 1776. 



March 10th, 1776 „ in March 28th, 1776. 



From the above experiment it would appear that a continued heat 

 from the time of laying, does not bring them in the least faster forward ; 

 and, indeed, would seem rather to retard it ; and that a certain degree 

 of cold continued for a considerable time was necessary. 



The coat of the egg is so hard and impenetrable, that in those which 

 did not hatch, although exposed to a whole summer's drought, very 

 little of their internal substance had evaporated ; and, when cut into, 

 the substance of the egg was moist and sweet; not putrified in the 

 least. 



Appearances after Natural Death. — "When the silk-moth is dead, we 

 find that the stomach is hardly to be perceived, and is only to be known 

 by the gut and vessels going into it ; and in some it is pushed back- 

 wards by the increase of the air-bag; but in many it still keeps the 

 attachment by the remains of the oesophagus. The testicles are almost 

 entirely wasted ; the vasa deferentia are still perfect. The air-vessels 

 become flat ; there is hardly any air in them. The bag at the anus is 

 much as when the moth was alive, full of a brownish-red fluid, with a 

 whiter chalky substance, which is specifically heavier than water. 



Although silk-moths do not fly in this country, it is to be supposed 

 they do fly where they are native. 



[Order Diptera.] 



The Large Blue-Bottle Ely \_Musca carnaria, Linn.]. 



Flies may be said to live on fluids, or such as may be raised by suction 

 or capillary attraction. The organs of digestion are attended with a 

 crop 1 . The organs of circulation and respiration are similar to those of 

 other flying insects. 



The oesophagus, when got to the neck, or through the head, has a 

 swell, or is surrounded by a thickish substance, probably glandular. It 

 there divides into two. canals ; one, and the smallest, passes across the 



1 [Hunt. Prep. Phys. Series, No. 596 (Musca pendula).] 

 VOL. II. 2 I 



