394 ON THE ORIGIN OF ENTOZOA 



and consequently, that we could scarcely pronounce that worms 

 are connate ; and he further urges, that those animals which 

 feed in dry, arid situations are never infected by them, and, on 

 the contrary, that those who seek their food in low and humid 

 districts are exceedingly prone to them. With great deference 

 to the opinion of this celebrated individual, I do not think his 

 hypothesis — " the eggs can only be developed in those situa- 

 tions in which we discover them" — by any means removes one 

 difficulty ; for I apprehend that if they were placed in the 

 bodies of different animals (I do not mean in those which 

 present the extremes of difference), that they would be hatched, 

 as it is termed, and take up their abode in them. But the 

 ovules, and these too in a very recent state, must be immedi- 

 ately deposited in animals furnished with the requisite degree 

 of temperature ; and as this latter is a condition essential to 

 the growth and development of the embryo worm, wherever it 

 may have been deposited, it admits of no delay in what we 

 may term its middle state, viz. the cold air and water. I am 

 led, from this train of reasoning, to view the hypothesis which 

 regards external communication as essential (whether it be 

 with dry or moist air, dry or humid ground) as an absurd one. 

 I shall have occasion to notice, presently, the influence which 

 humid situations may have in favouring the " verminous 

 diathesis." 



I have already pointed out the necessity of giving the 

 Entozoa a distinct place in the chain of living organized beings. 

 Their tender and delicate structure, their almost universal 

 inability to endure exposure to air and cold, render the warm 

 animal fluids essential to their vitality ; their very great mobility 

 and elasticity give them the power of contracting their bodies 

 into an extremely small space, of elongating them almost indefi- 

 nitely, of drawing them up into innumerable plicae, or folds, and 

 even of crawling along the intestinal canal. They are furnished 

 with contractile porules, or mouths for suction, with unciform 

 retinacula, by means of which they firmly adhere to sustaining 

 parts without injuring them ; and so tenacious is their hold, 

 that when once firmly fixed, they will allow their bodies to 

 break asunder rather than give way to any efforts made for the 

 purpose of disengaging them. Some of them possess an 

 absorbing function, by means of which nutritious fluids, easy 

 of assimilation, are conveyed into the body ; in short, we see in 



