1921] Riley: Guide-posts to Medical Entomology 165 
which the worm can mature. This case has acquired added 
significance through recent discoveries that a related worm, 
developing in the cockroach, is capable of causing cancer of 
the stomach in rats. 
Two years later, in 1869, Leuckart and his student Melnikoff, 
discovered in the body cavity of the dog louse, cysts which 
proved to be those of the double-pored tapeworm of dogs, the 
commonest species infesting these animals. In reality, the worm 
infestation is more common than is the louse infestation, a 
fact which was puzzling until 1888, when Grassi found that the 
dog flea also serves as an intermediate host for the worm. The 
cysts are so minute that as many as fifty have been found in a 
single flea. The dog becomes infested solely through swallowing 
an infested louse or flea. In rare cases this tapeworm is also 
found as a human parasite, usually in children. 
We have seen that Stein early suggested that insects might 
serve as intermediate hosts for tapeworms of various animals. 
Of a number of such cases worked out may be cited that of 
Hymenolepis diminuta. This parasite of rodents and occasion- 
ally of man is noteworthy for the number and wide range of 
arthropod hosts in which it may develop. There have been 
reported the meal-infesting lepidopter Asopia farinalis, the 
Forficulid, Anzsolabis annulipes, two tenebrionid beetles and 
three fleas. Recently, there was brought to my attention 
evidence that the larve of this same tapeworm may develop 
also in myriapods. 
An exceedingly common disease in many tropical and sub- 
tropical countries is elephantiasis, a disease marked by an 
enormous swelling of the extremities or affected parts. An 
apparently isolated endemic center is Charleston, S. C. Typical 
cases are shown by the lantern slides, the second of which is 
from a Japanese makimona of the 12th century. Though several 
conditions may give rise to this disease, it is most commonly 
due to the presence in the lymphatics of parasitic roundworms, 
upwards of four inches in length. These discharge living larve 
which are to be found in the blood stream. The life history is 
especially significant because it is that of the first human 
parasite found to be dependent upon a mosquito for its devel- 
opment. The larve were first noted in 1863, and in 1872 Lewis 
recognized that the blood of man was their normal habitat and 
