P. Manson-Paiir and N. H. Fairley 41 
a single tube which extends to the posterior extremity; bifurcates once more, 
and opens on the tip of each bifurcation. 
The deportment of the cercaria appears to be as follows: it generally swims 
with the expanded tail uppermost, and may be seen resting on the surface 
with the forks spread almost at right angles to the rest of the tail. When many 
cercariae are present in a sample of water they arrange themselves at regular 
intervals from one another throughout the different strata. Should the surface 
of the water then be disturbed, the cercariae immediately become active, and 
by vibratile motions of the tail make their way to the point from which the 
disturbance commenced. 
Oxygen is necessary for their existence, and for this reason cercariae put 
up in hanging drop preparations in an air-tight vaseline compartment die 
with much more rapidity than those kept for a similar time in open glass 
jars. 
The cercariae of S. japonicum, according to Leiper and Faust, are of a 
smaller size than those of S. haematobium and mansoni, and as in the latter 
species the whole body is covered with minute spines. The oral sucker is 
enormously developed, occupying almost the anterior third of the body. At 
the lip of the sucker there is a series of small tubercles and, according to Faust, 
the salivary-mucin glands consist of five pairs with acidophilic protoplasm 
arrayed around the ventral sucker. 
Mode of Entry into Host. 
We already know that once ejected from the intermediate host, the cer¬ 
caria has but from 24 1 to 36 hours in which to come into contact with the skin, 
or mucous membrane of the upper alimentary tract of man, its definitive host. 
The actual method by which penetration of the skin or mucous membrane 
takes place is still under investigation. Two factors are, however, probably 
concerned: 
(1) The secretion by the cercaria of some chemical substance which has 
the property of dissolving the inter-cellular substance between the epithelial 
cells. 
(2) The power which the cercaria possesses of rapidly altering its shape 
by contraction or relaxation of its body. 
Leiper demonstrated the process by immersing a mouse for half an hour 
in water heavily infected with cercariae, and subsequently embedded it in 
paraffin. Microscopically, sections showed cercariae in various stages of transit 
through the unbroken skin. At the end of the half hour only a few of the 
cercariae were left in the water, but a great number of detached tails were 
observed. Warmth would appear to be the main factor in attracting the cer¬ 
cariae to the skin. 
1 In actual practice during the summer months in Cairo wo found that the majority died after 
12 hours. 
