258 OUR HOUSEHOLD INSECTS 



clothing, the greater looseness of which renders them 

 easier subjects for the fleas to gain access to, and there- 

 fore to operate upon. 



In consequence of the compression of the body and 

 the comparative transparency of the skin, many details 

 of internal anatomy may be made out in the living flea, 

 if it be examined under the microscope with good illumi- 

 nation by transmitted light. The tracheae, or breathing 

 tubes, can thus be very easily traced, even down to 

 many of their finer branches ; and the large trunks that 

 traverse the length of the body are especially conspicuous 

 objects ; large branches may also be easily seen running 

 down the legs. If the flea is confined so that it can 

 only move slightly, the contraction of the muscles, 

 especially in the coxae, can be watched without any 

 difficulty, as any little twitchings occur in the legs. 

 A living flea is a very pretty object when viewed with 

 polarised light. 



The original photographs of which Plate Y. is a re- 

 production were obtained from specimens prepared for 

 the microscope, and therefore completely flattened. In 

 the process of mounting, the thoracic segments un- 

 avoidably become slightly dislocated from their natural 

 position : this is especially noticeable in the male. The 

 greater part of the contents of the body also have been 

 dissolved out, in order to increase the transparency of 

 the object, and hence very little of the internal anatomy 

 can, in these specimens, be seen. The most prominent 

 object in this connection is the reproductive apparatus 

 of the male : the bars and coiled threads at the hinder 

 extremity are all parts of these organs, and are really 

 internal in position, though they hardly seem so. The 

 coiled threads are attached to the part of the organ that 

 can be protruded. 



