Packard.] 352 T^ay 2, 
which we need for the performance of a certaui movement a ])oint 
of support or leverage, the greater the hitter the greater being the 
power, acts in this case. The muscles which pass into the coxae 
of the hind legs are in tlie flea attached to the entire inner 
surface of the notum and the wing-like scales of the metathorax, 
— a fact which gives the fleas in springing such a preeminence 
over other insects. On the other hand, the same cause has 
brought about the great development of the pleurae (wing-like 
scales) and of the anterior diaphragm of the metathorax, since 
these serve as the chief points of attachment of tlie springing 
muscles. Finally the coxae in their unusual development, due to 
the same cause, occupy almost the entire under surface of the 
meso- and metathorax, and thus have produced an atrophy of the 
corresponding sternites, or their removal within the thorax." 
Wagner sums up the other results of his observations, espe- 
cially in Vermipsylla, at the end of his essay, some of which I 
quote : — 
"The eudocranium is represented by two outgrowths of which that 
near the eyes projects from the walls of the head, bends back towards the 
thorax, and reaches the hinder side of the head, with Avhich it unites." 
"The opening of the mouth is bordered above by the maxillae, beneath 
by the labium." 
"The maxillae of fleas form a three-sided pyramid in which the muscles 
pass through an opening at their base." 
"The pharynx serves as a sucking organ which is moved by the 
muscles which pass from its walls upwards to the top of the head and 
downward to the inner skeleton of the head." 
"The abdomen of fleas consists of nine complete segments. The 
sternite of the first segment is united with the wing-like scales." 
"The eighth abdominal segment of the male consists of a ventral and 
a dorsal plate. The eighth abdominal segment of the female is formed 
of two dorsal and two ventral pieces; in Vermipsylla the dorsal and 
ventral half-pieces of corresponding sides are consolidated with each 
other. 
"The last, ninth, abdominal segment, becomes in both sexes of Vermip- 
sylla formed by a dorsal and ventral plate. 
"The anus of fleas is separate from the sexual opening at the end of 
the ninth segment, betAveen tlie ventral and dorsal plates. 
"The sexual opening, bounded on the side and beneath by the eighth 
sternite (in the male by the forceps of the clasping apparatus) and above 
by the ninth sternite, consequently lies on the ventral side of the 
abdomen. 
"The clasping apparatus of Vermipsylla $ is formed by a pair of 
forceps which closely resemble those of a crab." 
