344 



numbex" of Helminths, which are found encysted in tissues in a 

 kind of chrysalis state, are all in the early stage of development 

 of a more perfect animal. 



The eggs, therefore, are the only means which nature makes 

 use of in the preservation of Ilelminths. As all animals are 

 not the proper habitat of every species of Helminth, but, on the 

 contrary, as every species has provided for its nidus either one or 

 a few species of animals, the determination of the species adapted 

 for the development of each kind of worm is of great interest and 

 importance. 



The number of eggs produced by each individual Helminth is 

 immense. They are to be estimated by thousands ; and, in those 

 species where the development is more complicated through 

 change of habitat, the calculation is to be made by tens of thou- 

 sands and millions. According to an average estimate, made 

 from the number of human tapeworms in a certain district, and 

 from the number of eggs they produce, we should judge that, 

 from a million of eggs, scarcely one tapeworm reaches its full de- 

 velopment. More than half of a million of eggs may perish 

 before the embryo is hatched : but, provided every individual 

 worm produces a million of eggs, the existence of the species is 

 preserved, if only one egg out of a million becomes fully developed. 

 The loss of this great amount of germs seems, at first sight, to be 

 extravagant ; yet, here as everywhere, nature studies the strictest 

 economy, that is, effects with the smallest possible means the great- 

 est possible results; and exhibits the most profound and accurate 

 calculation of chances, — a profundity and accuracy extremely ditii- 

 cult to be imagined when the innumerably vai'ying conditions are 

 taken into account. The number of individuals living at a given 

 time may vary ; but, for any considerable length of time, there is 

 no variance ; otherwise there would be a disturbance in the numer- 

 ical relation of animals, and consequently in the order, beauty, and 

 variety of nature. For if, instead of one, three or four out of 

 the million eggs were to arrive at maturity, the number of Hel- 

 minths would be three or four times as many as at present, and, in 

 succeeding generations, hundreds and thousands of times as many. 

 In those orders of Helminths, where the development is the most 

 complicated, as in Tapeworms and Suckworms, the individuals 

 are hermaphrodites and capable of propagation by themselves, 



