476 Studies in the Theory of Descent. 



It cannot be stated in objection that there are 

 many moths which fly by day. It certainly 

 appears that no great structural change is necessary 

 to confer upon a Lepidopteron organized for noc- 

 turnal life the power of also flying by day ; but 

 this proves nothing against the view that the 

 structure of the butterflies depends upon adap- 

 tation to a diurnal life. Analogous cases are 

 known to occur in many other groups of animals. 

 Thus, the decapodous Crustacea are obviously 

 organized for an aquatic life ; but there are some 

 crabs which take long journeys by land. Fish 

 appear no less to be exclusively adapted to live in 

 water; nevertheless the "climbing-perch" (Anabas) 

 can live for hours on land. 



It is not the circumstance that some of the 

 moths fly by day which is extraordinary and 

 demands a special explanation, but the reverse 

 fact just mentioned, that no known butterfly flies 

 by night. We may conclude from this that the 

 organization of the latter is not adapted to a 

 nocturnal life, 



If we assume 2I that the Lepidopterous family 



of Natal," Mr. W. D. Gooch states that he never saw Melanitis, 

 Leda, or Gnophodes Parmeno on the wing by day, but generally 

 during the hour after sunset. He adds : " My sugar always 

 attracted them freely, even up to loor n p.m." Many species 

 of HesperidcB are also stated to be of crepuscular habits by this 

 same observer. See " Entomologist," voL xvi. pp. 38 and 40. 

 R.M.] 



11 I only make this assumption for the sake of simplicity 



