THE INTRODUCTION. 



The study of the whole order of Lepidoptera has con- 

 vinced me that the genitalia throughout the order have 

 been developed on the lines of one common plan, which 

 has been so far modified as to suit the requirements of each 

 individual group. Some of the parts may be atrophid or 

 even absent, others decorated with elaborate armature, 

 others much displaced, others now free, now fused together, 

 but the main features remain common to all the groups. 

 Thus it is true to say, though this general statement needs 

 some qualification, that the main characters of the male 

 genitalia in the Geometridce are very similar to those in 

 the Noctuidce. The different organs may be conveniently 

 divided into two parts, the external and the internal. This 

 division is well shown in the curious specimen of 

 Hydrcecia, captured by Mr. Burrows, the body of which 

 was prepared by him and figured in the " Entomologist's 

 Record," Vol. xxiv., p. 171. 



The external part consists of : (i) The Uncus, 

 which is attached to the dorsal region of the tegumen. 

 (ii) The Tegumen, which consists of the ninth and 

 possibly part of the tenth abdominal segments, (iii) The 

 Saccus, which is a development of the base of the tegumen. 

 (iv) The Valvce, which form a pair of lateral flanges, 

 articulated to the tegumen. (v) The Anus with its 

 armature, (vi) The Transtilla, a cross-bar uniting the 

 costae of the valvse. 



The internal part consists of The Penis with its 

 armature. The seventh and eighth abdominal segments 

 also possess characters which I consider to be of sufficient 

 importance for inclusion in the descriptions of the text. 



