HYDATIDS. 157 



when the fluid is clear, or have altogether disap- 

 peared, lead us to infer that they spring from those 

 egg-like bodies ; and when we find thousands of 

 perfect, but small hydatids, these worms being 

 absent, we are induced to conclude that these are 

 probably the worms in a stage of perfect develop- 

 ment, structurally considered, and which, by their 

 growth, would ultimately burst the parent cyst, and 

 so escape. Let us, then, assume all this, (it is at 

 least probable, if not proved,) and then endeavour, 

 without having recourse to the unphilosophical 

 theory of equivocal generation, to account for the 

 presence of hydatids in the brain of the sheep or 

 ox, or in any other enclosed portion of the animal 

 system. 



Let us conceive of an animal dying from the 

 mischief caused by a hydatid in the brain, which 

 hydatid is laden internally with myriads of granules, 

 the presumed germs of perfect creatures. Now, it 

 is granted that the parent entozoon perishes, but it 

 ' does not follow that the granules or eggs which it 

 contains also lose their vitality. In an animal so 

 low in the scale of being, organically lower than 

 even plants in general, and which is destitute not 

 only of a distinguishable nervous system, but also 

 of vessels of circulation, it is by no means going 

 too far to consider the microscopic eggs as still 

 retaining their vitality. But how long will they 

 do so ? Probably for many years. The seeds of 

 plants have been known to retain their vitality for 



