TBEMATODA 



47 



gyrating animalcules were lodged in ovo within the blood-vessels 

 of their human host. From persons who are infested, myriads 

 of these eggs of Bilharzia daily make their escape during the 

 act of micturition ; and, when this act is accomplished by the 

 host out-of-doors, it is easy to perceive how readily the ova may 

 be subjected to conditions favorable to the development of larvae. 

 The direct passage of the urine into any considerable receptacle 

 of natural or fresh water would in a few minutes ensure the 

 hatching of all the eggs ; and in the absence of any such direct 

 aid to development, the accidental occurrence of a shower of 

 rain would, in all localities where the Bilharzia disease is 

 endemic, readily transfer the ova into ditches, ponds, rivers, 

 lakes, and ultimately, perhaps, even into the sea itself. 



FIG. 15, Egg of Bilharzia, with the shell still adhering 

 to the escaped ciliated embryo. Original. 



FIG 16. Ciliated embryo of Bilharzia in 

 the act of dying from the escape of its 

 sarcodic contents. Original. 



The behaviour of the embryo under the action of reagents of 

 various kinds is remarkable. Thus, when on the 5th of Sept., 

 1870, I placed some ova in brackish water, of the strength of 

 two parts of fresh water to one of pure sea-water, their contents 

 were readily developed, though the escaping embryos did not 

 swim vigorously. When again I placed some other eggs in 

 pure sea-water, their contained embryos became instantly trans- 

 fixed, the vibratile cilia of the head being rigid and motionless. 

 At first I naturally concluded that the embryos were killed 

 outright ; but, to my great surprise, the shock passed away in 

 about half an hour, when they revived and were soon afterwards 

 hatched. One of the larvae thus set free carried off several of 

 the loose intra-chorional globules which had, during the period 

 of transfixion, become firmly adherent to the ends of the caudal 

 cilia. Here I may remark upon a decided difference observable 



