CHARACTERS OF THE DIPTERA. 27 



it is impossible to judge of the intellectual functions of an insect. 

 The manner in which the blow-flies and their near allies, the 

 house-flies, have made themselves at home with man speaks 

 for their power of adapting themselves to new and varied con- 

 ditions. They are cunning, wary and easily alarmed, and, 

 except when benumbed with cold or heavy with eggs, know 

 well how to avoid danger. They appear to me far more clever 

 in this respect than the bees or wasps. 



The Diptera are specifically and numerically the most abun- 

 dant of all insects, and exhibit a wide range in organisation, so 

 that we may arrange them in lower and higher groups, or, to 

 use the language of the evolutionist, we may regard the order 

 as consisting of ancient and modern forms. The members of 

 the lower subdivision of the order retain a larval condition 

 similar to that of the Hymenoptera,Coleoptera,and Lepidoptera 

 in their most differentiated form, and undergo a gradual meta- 

 morphosis. The larval skin splits along the back for the escape 

 of the nymph, and some spin a silken cocoon for its protection : 

 such Diptera are said to be orthoraphic. 



The higher Diptera have a larva which is apparently headless; 

 they form a pupa, the external covering of which is the modified 

 larval skin, which splits by a circular fissure, for the escape of 

 the imago : such Diptera are said to be cycloraphic. In these 

 the nymph is developed rapidly within the larva after the com- 

 plete histolysis of all its tissues, so that the perfect insect is 

 more nearly related to the embryo than to the larva, and 

 the nervous system of both larva and imago is highly concen- 

 trated and exhibits great complexity. 



The Larvae of the Diptera. Dr. J. R. Schiner [11] gives the 

 following description of the dipterous larva. He says : ' They 

 have as a rule an annulate form, and may be divided into 

 two easily distinguished groups : those which have a distinct 

 chitinous head capsule, cuccplmlce ; and those in which the head 

 is scarcely distinguishable, accplialas. The latter, which are 

 designated " headless," are devoid of eyes, antennas, and feet. 

 This form of larva is known as a maggot. The dipterous 

 larvae have usually thirteen segments, of which the head is the 



