DR SHARP ON IN8ECTA. 247 



as to their ancestors having formerly possessed wings is by no 

 means satisfactory, and from a practical point of view there is a 

 decided advantage in placing under a separate category the forms 

 that are believed to exhibit either " acquired ametabolism," or ac- 

 quired winglessness. 



In the Anapterygota the two groujxs Mallophaga and Anoplura 

 exhibit but little metamorphosis, while on the contrary the fleas 

 have a very rapid development, accompanied by a metamorphosis 

 complete except as to the appearance of wings ; as the young of the 

 flea has no trace whatever of wings externally, and as it is possible 

 that there is some slight trace of them in the subsequent instar, it is 

 highly probable that a critical examination will shew that these 

 insects should be treated as derived from the Endoptcrygota ; in 

 which case those who advocate the view of acquired ametabolism 

 will be able, with considerable show of probability, to point to 

 this group of insects as exhibiting an early stage of this process : 

 the ametabolism being actually limited to the want of wings. 



On the other hand it is nearly certain that if Mallophaga and 

 Anoplura are really exponents of an acquired ametabolism, they 

 will be found to be derived from exopterygotous insects. 



The group Exopterygota consists of those insects that actually 

 develop the wings outside the body, but it includes a few wingless 

 insects that are undoubtedly closely allied to winged. A most 

 interesting condition is found in the small division Embiidae, where 

 the females never have wings, while the males acquire them, though 

 in other respects remaining almost in the condition of wingless 

 insects. Although very little is known as to Embiidc3e, the notes as 

 to its development, recently contributed by Mr W. F. H. Blandford, 

 shew that it is exopterygotous. 



The Exopterygota exhibit most of the kinds and degrees of 

 metamorphosis. We have already alluded to the fact that the 

 female Embia is almost without metamorphosis, while the male ac- 

 quires wings, but remains almost without some of the other features 

 of metamorphosis. In the Hemiptera we find that these sexual 

 differences as regards metamorphosis exist amongst Coccidae to 

 a much greater degree, the female exhibiting but little meta- 

 morphosis, while the male passes through a complex metamor- 

 phosis. 



The Endoptcrygota include an enormous majority of the existing 

 forms of insects : if we estimate the number of known species of 

 Hexapod insects at 250,000, the number of Endoptcrygota is 90 per 

 cent, or more, of this. 



The Endoptcrygota are almost entircl\' holometabolous, the only 

 exceptions being a certain number of species in which the female 

 exhibits an arrest of development, departing very little from the 

 condition of the larva ; as an instance we may mention the females 

 of certain Coleoptera of the family Malacodermidae. 



On the table there is also shown the elements of what is known 



