26 
straw where the eggs are deposited. Hence when a number of rats 
are in the same cage the mites may visit a different animal each night. 
It is an easy matter to cause the mites to get upon the rats in the 
daytime by stirring the straw about in the cage and making the rats 
move about. In small cages, such as the glass jars used in the labo- 
ratory for holding single animals, the mites behave differently, espe- 
cially if sand or sawdust is placed in the bottom. The rat moving 
about frecpiently in the narrow cage keeps the mites constantly 
disturbed, and they remain upon their host all the time and may be 
found in large numbers upon the back of the animal near the root of 
the tail. The female mite after feeding leaves the rat to deposit her 
eggs, which are laid one at a time, in damp straw. Each egg con- 
tains a well developed embryo. After hatching, the six-legged larva 
in a few hours moults and becomes a nymph with eight legs. The 
nymphs, though active, are seldom found upon rats and do not appear 
to suck blood. The nymphs after two moultings become adult. The 
young adult females (at first colorless) seek the host, and draw blood 
from small wounds made by the maxillse or mandibles. TVIien fully 
grown they are larger and brovui in color. The males do not suck 
blood, but feed upon animal or vegetable detritus. They are few in 
number upon rats. The average length of life of the female mite is 
about six weeks. During this period a number of feedings of rat's 
blood are necessary to proHde material for the development of the 
embryos. 
EXTERNAL ANATOMY OF LELAPS ECHIDXIXUS. 
Technique. — In view of the small size of the mite nearly all the 
details of structure of the exo-skeleton may be determined by exam- 
ination with low powers of the microscope after a few minutes immer- 
sion of the live mite in alcohol. 
For brief study the specimens may be mounted in water on a slide 
with a cover glass. For examination vdth liigher inagniHung powers 
mites must be macerated in caustic jiotash to render them more 
transparent. The details of the mouth parts may often be studied in 
live specimens to advantage, the capitellum being then more markedly 
protruded. 
Gexeeae body coxsteuction. — The head region or cajnUTlum 
(pi. iv) is distinctly separated from the thorax and contains the mouth 
parts and certain appendages. The fused thorax and abdomen are 
covered dorsally by the scutum, a single cliitinous plate. On the 
inferior or ventral surface are three cliitinous plates — sternal, genital, 
and anal. The sternal plate serves as a point of attachment for the 
legs. The latter are eight in number (four pairs) and are composed 
of six articles, terminating in two booklets and a sucking disk. 
