262 



ENTOZOA. 



remarked, they are particularly liable to occupy tlie liver and lungs 

 of the same animal ; these viscera being sometimes riddled, as it 

 were, with separate cysts. They do not usually protrude much 

 beyond the common surface of the infested organ, but they lie, 



Fia. 56. — Portion of the liver of a pig, with an hydatid cyst laid open to display several groups of 

 proliferating daughter vesicles. Natural size. — Busk. 



for the most part, imbedded within its parenchymatous substance. 

 Selecting any ordinary fresh example of the exogenous or of the 

 simple kind, and laying the tumour open with a scalpel, we notice 

 in the first instance an escape of a clear transparent amber-coloured 

 fluid, which previously caused the distention of the hydatid sac. 

 If the tumour is large, this escape will probably be followed by a 

 falhng in, as it were, of the gelatiniform hydatid membrane, in 

 which case the external adventitious investment or true fibrous 

 cyst will be laid bare at its inner surface. If the hydatid be next 

 withdrawn from the cyst, it will be seen to display a peculiar and 

 characteristically tremulous motion, at the same time coiling upon 

 itself wherever there is a free cut margin (Fig. 3, Plate XIII). 

 Further examination of portions of the hydatid will show that we 



