384 Parasitic Worms 
the former Ransom has demonstrated that the larval Nematode found as long 
ago as 1859 by Carter in the common house-fly in Bombay and named by him 
Habronema muscae is actually the larval stage of a parasite of the horse, 
closely allied to a similar horse parasite, Spiroptera microstoma described in 
1866 by Schneider. The occurrence of this larval Nematode in the house-fly 
and the stable-fly (Stomoxys calcitrans) has also been recorded in Australia by 
Harvey Johnston (1912). 
The life-history of this parasite is one of the most remarkable which has 
been brought to light within recent years. It furnishes yet another instance 
of the important part which house-flies play in the transmission of disease. 
So far as one can judge from observation and experiment the life-history 
appears to proceed on the following lines. The eggs or larvae of Habronema, 
occurring in the horse manure, are ingested by the larvae of the house-fly. 
During the metamorphosis of the fly the larval worms find their way into the 
Malpighian tubules and thence in the adult fly they migrate into the proboscis. 
When the fly applies its proboscis to an open sore or to the lips or conjunctivae 
of the horse the larval worms escape from the fly’s proboscis and invade the 
abraded tissue. Thence the worms migrate through the body of their host and 
eventually find their way into the intestine. Infection with this worm is thus 
curiously correlated with the occurrence of summer sores. We owe the eluci¬ 
dation of this remarkable life-history chiefly to Railliet and Henry (1915), van 
Saceghem (1917), Hill (1918), Teppaz (1919) and Roubaud and Descazeux (1921). 
The most recent discovery of prime importance to human medicine is that 
of the life-history of Loa ( Filaria ) loa. This is the result of some excellent 
experimental work by A. and S. Connal (1922) in Lagos. Following one of 
Manson’s intuitive suspicions they devoted attention to the Tabanid flies, 
Chrysops silaria and C. dimidiata in which they have been able to demonstrate 
that the worm passes its larval life. The larvae develop in the abdominal 
muscles and connective tissue of the fly and eventually in their infective state 
migrate to the fly’s proboscis. 
The life-history of another worm of the Spiroptera group, Gongylonema 
scutatum , a parasite of sheep and cattle, has also been dealt with by Ransom 
and Hall (1915, 1917) who found that the larvae live in dung-beetles of the 
genera Aphodius and Onthophagus and in the croton bug (Ectobia germanica). 
The allied parasite, Gongylonema pulchrum, of the pig also develops in the 
croton bug. The first observations on the larval host of worms of this group 
were made by Leuckart (1867) and Marchi (1871) in the case of the rat para¬ 
site, “ Spiroptera ” obtusa , the larva of which was found to occur in a beetle, 
Tenebrio molitor. 
Another strikingly able paper is that of Veglia on the anatomy and life- 
history of the Nematode, Haemonchus contortus. The developmental history 
of this important parasite of sheep is worked out in great detail and the result 
is a model of what such experimental investigations should be. It is un¬ 
doubtedly one of the best pieces of work of its kind. 
