LIVER FLUKE. 209 



length, that is, almost too minute to be visible to the 

 naked eye, and in shape not unlike a sugar loaf. In 

 the centre of the largest end is a peg-like projection 

 which is used as a boring tool, and can be withdrawn, 

 or greatly thrust out, at pleasure. 



The embryo darts and circles about in the water, 

 large end foremost ; and if in the course of its move- 

 ments it meets with the Water Snail {Limnceus tniii- 

 catidus), it at once commences operations. It inserts 

 its borer, and, spinning round and round on itself in 

 the water so as to work the point in like a centre-bit, 

 squeezes its way into the substance of the snail. 

 Here the embryo settles into almost still life, and 

 changes into an oval form, which, when complete, is 

 known as a sporo-cyst, that is, a " cyst," or a bag, or 

 bladder, of germs. Within this bag, so to call it, 

 about ten germs develop, known as " redife."* Each 

 redia as it is developed makes its way out of the sporo- 

 cyst, and being furnished with a mouth and intestine, 

 and two projections that answer the purpose of legs,. 

 it feeds on, and makes its way about within, the body 

 of the snail. 



Up to this point it will be seen there are four dis- 

 tinct stages of Fluke life, — the egg; the free swimming 

 embryo ; the quiet form of the sporo-cyst, altering to a 

 mere bag of developing germs ; and the germs called 

 redise, free from the bag, and feeding on the Snail, 

 which ultimately (for the most part) sinks under the 

 parasitic attack. 



Continuing the history from the same observations, 

 it is shown that in each of these redire there form (as 

 in the sporo-cyst before mentioned) a number of 

 germs, but different to these in shape. The germs 

 (the redise) that formed in the sporo-cyst are long and 

 narrow, about the sixteenth of an inch in length, and 

 about one-fifth of their length in width ; but the 



* This name is given after the Italian anatomist, Eedi, see Prof. 

 Thomas's paper previously referred to. 



