5 

 stages of development and also in large numbers. Moreover I had 



T . . . . 



a good chance though the kindness of the authorities of the British 

 Museum (Natural History) to examine the large collection of Pendens 

 in the Museum. From the study of these materials I found that the 

 most reliable point about the determination of species is the compari- 

 son of the structure of the external, secondary sexual organs, the so- 

 called the petasma and the thelycum, though differences of their 

 structure are sometimes very slight in case of closely allied species. 

 The chief difficulty in identification, however, lies in the incompleteness 

 of original descriptions and figures. 



