210 



THE YOUNG NATURALIST. 



Others again have produced an immense number of different forms varying in 

 all kinds of ways, yet establishing no permanent or constant variety. But 

 wherever there are two well marked forms of an insect, whether sexual or 

 otherwise, the absence or rarity of intermediate forms seems to require ex- 

 planation. 



The greater importance of the female in perpetuating the race need scarcely 

 be commented on. After they have paired, the male has no more to do, and 

 his immediate death is of no consequence. But the female has yet her ova 

 to deposit, and until this has been accomplished satisfactorily the object of 

 her existence is not fulfilled. That all differences existing between the male 

 and female are, or have been, for the advantage of the latter, there can be no 

 doubt. It may not be possible to explain, or understand how certain differ- 

 ences are advantageous. It is even possible that a form brought into existence 

 under one set of circumstances, may continue to exist under changed con- 

 ditions, thus rendering the problem still more difficult of solution. In some 

 cases the importance of the preservation of the female has led to the produc- 

 tion of more than one form of it. This curious phenomena was unnoticed, 

 though several cases occur in Britain, and more in Europe, until it was 

 observed that certain exotic butterflies, believed to be distinct species, and of 

 which no males were known, were only forms assumed by the females of 

 other species. Thus Papilio pammon has a male and female resembling each 

 other, and a second form of the female long known as Papilio poh/tes. 

 Another butterfly far from rare in India, &c, known as Papilio romulut, and 

 of which no male is known, is probably, almost certainly, a third form 

 assumed by the female of P. pammon. Other Indian or Malayan illustra- 

 tions might be given, but perhaps that best understood is the case of Papilio 

 turnus, a common North American butterfly. North of Latitude 37°, 

 Papilio turnus is found with males and females, resembling each other very 

 closely. South of this latitude, Papilio glaucus, a very different looking 

 butterfly occurs, and was long believed to be a distinct species, but no males 

 of it are known, and it is now well established as a dimorphic form of 

 P. turnus. To the South of latitude 42° all the females are of the dark 

 Glaucus form. North of Latitude 37° they are all of the yellower form. In 

 the intermediate zone, both these varieties occur, and more singular still, 

 both forms have been bred from the same batch of eggs. In our own country 

 we have no such well marked illustration of dimorphic or trimorphic species 

 as these, but Colias Edusa with its second form of the female, Helice ; C. 

 Hi/ale with its second female Pallida ; Argynnis Paphia with its well-known 

 form Valezina, may be named as instances that home collectors may obtain 

 for their own study. 



