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to shelter himself under the example of nature. One thing we can 

 do, we can appeal to her to warn him of the dire consequences of 

 parasitism, of which crime she is a stern and invariable Punisher. 

 She deprives the bats and insects of eyes if thev shun the light of 

 day, and retreat into the darkness of caves ; and similarly she has 

 deprived the Hermit Crab of his shell and one of his claws and 

 the Sacculina of well-nigh everything it once possessed. The 

 diagram shows you its capabilities in its youth ; it comes from the 

 egg endowed with three pairs of swimming organs ; as it moults 

 it becomes enclosed in a thin bivalve test or shell ; then by means 

 of the hooks which have now appeared on its front limbs it fixes 

 itself on some unfortunate hermit who happens to be changing his 

 habitation ; " the sight of means to do ill deeds makes (another) ill 

 deed done," after which the Sacculina subsides into quiescence. 

 " Corpulent, blind, legless cripples, their existence is more pre- 

 carious than that of the most miserable, mutilated beings found in 

 our cities, they only live on the blood of the neighbour which gives 

 them an asylum. Yet when they first quit the egg they are all 

 free ; they trisk, they swim with the rapidity of lightning, and at 

 the close of life we find them deformed, and crouched in some 

 living refuge, as if a foul leprosy had atrophied within them all the 

 organs which served as a means of communication with the outer 

 world." (Van Beneden). 



In the previous instances we note that the degeneration attaches 

 to the latter stages only of the animal's existence. We might 

 almost imagine, I do not know why we should not, that there is 

 still for each of them a possibility of regaining the lost ground, 

 still a chance for an upward movement in the battle of life, seeing 

 that the early stage is already a high one. There are other 

 Parasites, however, the degradation of which is far more thorough 

 and complete, since it is patent throughout the creature's whole exist- 

 ence. It is born a parasite, and it remains one till death. Like a 

 nation utterly irreclaimable and depraved, in which there is no 

 tendency or opportunity, not even the desire, in any one individual, 

 to reach up after better things. It is a degeneration of the whole 

 kind, species, or it may be genus. Hatched from the egg in the 

 body of a higher animal, it takes up its abode there permanently, 

 or it passes by a strange transmigration into the body of another, 

 higher still, maybe even into our own, and perfects itself there. 

 I am thinking especially of the internal parasites, the Entozoa, 

 whose life histories are as marvellous as any of those I have related. 

 The suitability of their organization for their functions is as com- 

 plete as our own "Without organs of sense or digestion, none of 

 which are needed, they are well supplied with those of prehension, 

 in the form of suckers and hooks, by means of which they attach 



