INTRODUCTION. XXI 



serves as an apparatus for locomotion; but scarcely 

 have they tried to use their delicate oars, before they 

 demand assistance, lodge themselves in the body of the 

 first host that they meet, -whom they abandon for 

 another living lair, and then condemn themselves to 

 perpetual seclusion. 



That -which adds to the interest inspired by these 

 feeble and timid beings is, that at each change of abode, 

 they change also their costume; and that when they 

 have reached the limit of their peregrinations, they 

 assume the virile toga — we had almost said, the wedding 

 robe. The sexes appear only under this later envelope ; 

 up to this period they^have had no thoughts of the cares 

 of a family. It has always been somewhat difficult to 

 establish the identity of those persons who frequent the 

 public saloons one day, and are found on the next in the 

 most obscure haunts, dressed as mendicants. Most of 

 the worms which have the form of a leaf or a tape 

 give themselves up to these peregrinations, and those 

 which do not arrive at their last stage, die usually with- 

 out posterity. 



It is interesting to remark that these parasitical 

 worms do not inhabit the various organs of their 

 neighbours indiscriminately, but all begin their life 

 modestly in an almost inaccessible attic, and end it in 

 large and spacious apartments. At their first appear- 

 ance they think only of themselves, and are contented 

 to lodge, as scolices or vesicular worms, in the connective 

 tissue of the muscles, of the heart, of the lobes of the 

 brain, or even in the ball of the eye ; at a later stage, 

 they think of the cares of a family, and occupy large 

 vessels like the digestive or respiratory passages, always 



