THE RAT-FLEA, CERATOPHYLLUS FASCIATUS BOSC. 447 



one method of preparation supplements the other. For staining 

 an alcoholic stain is preferable, since prolonged soaking in watery 

 stains might produce maceration and cause the object to become 

 detached again from the cover-slip. I have always used Gren- 

 adier's alcoholic borax-carmine, in which the objects are stained 

 for about five minutes, and then transferred to acidulated alcohol 

 (0*1 per cent, hydrochloric acid in 70 per cent, alcohol), in order 

 to extract all the carmine stain from the cytoplasm of the cells 

 and leave it only in the nuclei. If the stain be not thoroughly 

 extracted in this way the preparation will be very opaque, and 

 I find it best to leave the objects in the acidulated alcohol for about 

 forty-eight hours, changing the fluid occasionally. I believe this 

 method could be improved upon, and that Mayer's alcoholic 

 paracarmine * would give a more transparent stain, and one 

 more easily extracted. Some of the well-known haematoxylin 

 mixtures would probably also give good results. 



The stained or unstained preparations are then finished off by 

 passing them into absolute alcohol, then into oil of cloves or any 

 other of the ordinary clearing reagents, and finally into Canada 

 balsam. The cover- slips can be mounted over well-slides or 

 preferably, in my opinion on ordinary slides, with the precau- 

 tion of supporting the corners of the cover-slip on wax feet or in 

 some other way, in order that the objects may run no risk of 

 being crushed between slide and cover-slip. 



I will now proceed to set forth some of my observations on the 

 anatomy of the flea, noting, as a preliminary, that all my state- 

 ments apply to the common rat-flea, Ceratophyllus fasciatus y 

 the only species I have dissected. Other species of flea may 

 perhaps show slight differences in some points. 



It is also my pleasant duty, at this point, to express my warm 

 thanks to Miss Mabel Rhodes, artist at the Lister Institute, for 

 kindly executing the drawings of my dissections which accompany 

 this paper. They were all drawn with the camera lucida from 

 the actual preparations. 



I. The Abdominal Nervous System. 



The method of dissecting out the abdominal chain of nerve- 

 ganglia has been described above. It is one of the easiest 



* For an account of these stains and how to prepare them see Bolles 

 Lee's well-known Vade-mecum. 



