SCHISTOSOMA MAN SON I 



587 



but Looss points out that even the presence of an egg with a true 

 miracidium is no evidence that the parent worms are ahve. 



Miracidium. — ^These eggs will simply die, unless they gain access 

 to water, in which they hatch, and the ciliated miracidium escapes 

 and swims about. In the so-called body cavity of this miracidium 

 there are genninal cells. 



Intermediate When miracidia are allowed to hatch out 



in water containing suitable and unsuitable snails, they crowd 

 round and enter the former, while they neglect the others. In a 

 short time all the miracidia have disappeared from the water con- ' 

 taining suitable snails. 



The snails which are suitable are those in which Leiper found the 

 development to proceed^ — -viz., Bullinus contortus Michaud, 1829; 

 B. dyhowskii Fischer, 1891; and B. innesi Bourguignat. In South 

 Africa Becker has experimentally implicated Bullinus (Physopsis) 

 africanus as an intermediary. 



Within these molluscs the miracidium makes its way into the 

 liver and becomes changed into a smooth-walled sac — the sporocyst 

 — from which are formed daughter sporocysts, and from these 

 cercariae. In any case the cercaria is the end of this stage, and is 

 alone the infective organism. 



In some of our experiments we so heavily infected our snails 

 that they died, but in nature this does not take place. 



CercaricB.—lf an infected snail is allowed to remain in clear water 

 it is amazing the quantities of cercariae which may escape therefrom 

 into the water and swim about. 



Infection, — -Leiper has shown that these cercariae may penetrate 

 the skin and infect animals. They may also penetrate the mucosa 

 of the mouth and throat; and then by gradual growth and differ- 

 entiation of the organs become male or female adult worms. 



Pathogenicity.— -It is usually the cause of urinary schistosomiasis, 

 or, as it is better known, vesical Bilharziosis, but occasionally it 

 may give rise to Bilharzial Dysentery. 



Schistosoma mansoni Sambon, 1907. 



Definition.— Schistosomum with spiny cuticle. Male with eight 

 small testes. The gut forks unite early, and hence the straight 

 intestine is long. Female with ovary in the anterior half of the 

 body. Uterus very short, with only one lateral-spined egg present 

 at a time. Vitellaria in posterior two-thirds of body. Development 

 of cercaria in Planorbis boissyi in Egypt and the Sudan, and P 

 olivaceus Spixin Brazil, and P. guadelupensis in Venezuela. 



Historical. — In 1851 Bilharz in Egypt noted that certain female 

 worms possessed uteri containing lateral-spined eggs, and later 

 Sonsino considered that these worms should be made into a species 

 separate from those with terminal-spined eggs, but nothing came 

 of it. In 1902 Castellani in Uganda noted that some patients had 

 only lateral-spined eggs in the faeces and no ova in the urine. In 



