50 [March, 



Thorax. The thorax of all fleas consists of three rings which are 

 subdivided into separate parts. The first ring, or prothorax, consists 

 of two parts forming a pronotum and prosternum. The second ring, 

 the mesothorax, consists of a dorsal portion, the mesonotum, and a 

 lateral and venti-al portion which is subdivided into three parts, the 

 mesosternum, the mesothoracic episternuni, and the niesothoracic 

 epimerum. The third ring, the metathorax, is again similarly divided. 



Abdomen. The abdomen of all fleas consists of ten segments, each 

 of which is divided into an upper and lower part known respectively 

 as the tergite and sternite. The first sternite, i.e., the sternite of the 

 first segment, however, is always missing. On each side at or near 

 the apical edge of the seventh tergite there are usually one or more 

 long hairs, known as the antepygidial bristles, which are of considerable 

 taxonomic importance, but in some species these bristles are entirely 

 wanting. The ninth tergite of the male is especially modified and is 

 best studied and described if it is assumed that it is laid out flat in 

 one plane. If this is done it would be observed that in the centre of 

 the segment is a highly specialised sensory plate generally known as 

 the pygidium ; further, that the two sides form what is usually known as 

 the clasper, bearing certain processes. In the fleas in which only one of 

 these processes is movable this process is called the finger (fig. 15, F). 



The females of all fleas possess a conspicuous receptacidum 

 seminis and in some cases two. This organ, which is highly chitinised, 

 can be easily seen in specimens which have been cleared in oil of cloves 

 (fig, 14, r.s.) 



The author desires to express his most sincere thanks to his friend 

 Dr. Jordan for the drawings which illustrate this article. 



Instructions for collecting the insects in question and notes on their 

 permanent preservation for study are given. Appended to this article 

 is a list — with fviU references— of all the genera and species which 

 have so far been found in the British Islands. 



Instructions for Collecting and Preserving 



SiPHONAPTERA. 



Fleas are found on mammals and birds, in the hair or feathers. 

 They are also found in their nests or holes. 



As soon as their host o'ets cold the fleas leave it. 



