INTRODUCTION. 



Before entering upon the descriptive part of the 

 work, it will be necessary to make some preliminary 

 observations, in order that those who have not worked 

 at this branch of entomology may be able to follow the 

 points touched upon. 



The organs constitute the last abdominal segments 

 of the insect, and are generally withdrawn into the 

 preceding segment, and hidden by an abundance of 

 scales and hairs, either on the last segment of the body 

 or on the organs themselves. Reference to various 

 writers shows that the segmentation of the body is still 

 unsettled. This is mainly owing to the author's speak- 

 ing of a certain segment, without describing its position ; 

 I have therefore thought it wise to definitely state the 

 plan I have followed. The body consists of a head, 

 three thoracic segments, eight abdominal segments, 

 which may have 6, 7 or 8 true spiracles, and the 

 genitalia. I treat these as a whole, notwithstanding the 

 opinion of some authorities that a division can be 

 discovered. Without throwing doubt upon their in- 

 vestigations, I consider it unnecessary to discuss the 

 matter, being unable to locate a definite segmentation, 

 and finding the matter unimportant from the point of 

 view from which I am describing the organs in this 

 work. 



