lO JOURNAL OF CONCHOLOGY. 



ON A PARASITE OF LIMN^A TRUNCATULA. 



By J. T. MARSHALL. 



. No. II of the "Journal of Conchology" recorded the 

 fact that a parasite of Limncea truncatula (Fasciola hepaticd) 

 caused the liver-fluke in sheep. The question is such an im- 

 portant one, though not so much to naturalists as to farmers, that 

 I think it deserves more than a few lines in a journal devoted to 

 conchology, and with your permission I will lay before your 

 readers a short account of the life-history of this parasite, which 

 caused the death, during the winter of 1879 — 1880, of no less 

 than three million sheep ! 



One of the half million eggs of one of these dire parasites, 

 lying in water or on damp grass, is duly hatched, and forthwith 

 there emerges, lifting the lid with which the egg is considerately 

 provided, a ciliated infusoriform embryo, about the 175th of an 

 inch in length. For it the future is grave indeed. Long the 

 work, short the time, and the opportunity fleeting; within eight 

 hours it must find its host or die, and that host is the tiny water 

 snail, Limncea truncatula. Accordingly, the instinct of the 

 embryo is unerring — so unerring, that when a large number of 

 them are put into water containing an assortment of water snails, 

 some forty of fifty embryo will, perhaps, bore their way into 

 each Limnma truncatula., inflicting fatal injuries; while the other 

 equally soft and inviting mollusks remain wholly unassailed. 

 The part they chiefly aim at, and mostly achieve, is the pulmo- 

 nary cavity of the snail, the one part that suits them to perfection; 

 indeed, if they have by accident located themselves in the harder 

 foot they survive for a few days only. They effect their entrance 

 by means of a bradawl-like projection of the head. This is 

 utilized after the following ingenious fashion. It is embedded 

 in the integument of the snail, its owner meanwhile spinning 

 round with great velocity, and thus, top-like, it gradually wedges 

 its way within. This achieved, the cilia are cast, the bradawl 



J.C., iv., January, 1883 



