REAUMUR 267 



Then we get a full description of the maggot/ includ- 

 ing such minute details as the anterior spiracles, which 

 are easily overlooked by an observer who has no means 

 of enlargement beyond a simple lens. He shows how 

 the pupa forms within the larval skin and is well aware 

 that the head and other appendages of the future fly are 

 telescoped into the body, from which they can be caused 

 to protrude by gentle pressure. A student who intends 

 to study all the details of the transformation would be 

 well advised to verify Reaumur's account as a pre- 

 liminary. He calls attention (Vol. IV, M^m. vii, viii) 

 to the peculiar method of pupation which is found in 

 the blow-fly. At first sight the pupa of such a fly seems 

 to resemble a Lepidopterous chrysalis, but it difiers 

 notably from all ordinary insect-pupae in one respect. 

 Reaumur tells us that when the maggot is full-fed, it 

 buries itself in the earth, if it can, and then contracts its 

 body until it assumes the figure of an elongate egg. 

 The larval skin is not cast, as in the pupation of a 

 caterpillar ; it persists as an outer defence, which we 

 shall in this abstract call the shell. Though it was soft 

 and flexible when it served as the skin of the maggot, it 

 now turns dry and firm ; its colour changes from white 

 to red, and ultimately to a deep maroon. The maggot 

 imprisoned within the shell is incapable of movement, 

 its head is withdrawn into the thorax, and the hooks, by 

 which it used to tear its food, are shed. Reaumur found 

 that when the shell was opened, a new and delicate skin, 

 the proper pupal skin, was found within it. Within this 

 inner skin he naturally expected to find a pupa, but in 

 a maggot which had just pupated he could discover 

 nothing but a milky pulp.^ Five or six days later he 



^Vol. IV, Mem. iii. 



^It has been ascertained since K^aumur's time that the larval tissues are 

 to a great extent consumed by phagocytes shortly before and after pupation, 



