that spread Disease. 35 



the eggs ; the thinness of the translucent shell is seen in the two 

 broken eggs. Slide B shows the larva, stained red wdth carmine 

 solution ; the head end is to the left. The body of the larva is seen 

 to be sparsely covered with stiff hairs or liristles, and there are no 

 eyes nor legs. Slide C shows an early pupa, shrinking in length 

 while still within the hairy larval skin. The first traces of the legs 

 can be seen. Slide D shows a later pupa, very transparent and 

 delicate in texture, owing to a reconstruction of all the internal 

 parts of the body which takes place at this period of development. 

 The legs are of considerable length, and the body is assuming the 

 size and shape of the flea. Slide E shows an adult male ; the 

 Ijody is now yellow, with an external hard casing of chitin, 

 produced into numerous hairs and spines. 



Eeturning to the middle of the Hall, the visitor will see in one 

 of the two sloping-faced table-cases an enlarged, coloured drawing 

 ( X 40) of a female specimen of the human flea, Ptdex irritans 

 Linn. The flea of man is larger and darker in colour than the 

 tropical rat-flea {Xenopsi/Ua cheopis), and has larger stigmata or 

 breathing pores, larger claws on the feet, and much larger eyes ; 

 the piercing mouth-parts, also, are stronger and broader. The 

 long bristle which in the rat-flea passes backwards across or near 

 the eye is much lower down in the flea of man ; and in the latter 

 there is no internal bar extending from the mid-coxa into the 

 thorax — this last feature can only be seen in specimens that have 

 been made transparent so as to render the internal structures 

 visible. Other differences between the species occur in the sexual 

 organs. 



Under the microscope placed on the West side of the Hall 

 near the entrance to Bay I. are shown twelve slides, of which nine 

 a)'e preparations of adult fleas of general interest. 



A is a male tropical rat-flea, Xenopsylla cheopis Eothsch. 

 (fig. 9). As already explained, this flea is common on rats (and 

 other rodents) in warm countries, having become almost cosmo- 

 politan in distribution. It is known to transmit the bacillus of 

 bubonic plague from infected rats to man, and is frequently terpied 

 the plague-flea. 



B is a male flea of the species Ctcnophthalvms agyrtes Heller. 

 This species of flea is common on rats, and also on field-mice, 

 stoats and weasels, in Europe. It is not known to transmit any 

 disease. It is distinguished from "A" by having no eyes, and by 



D 2 



