82 LIFE-HISTORY OF PARASITES. 



season of the coral polyps, myriads of microscopic embryos swarm in 

 the neighbourhood of the parent stock ; millions of these are washed 

 out to sea and on to dry land, and perish, or fix themselves in posi- 

 tions where they cannot grow ; but if only a single one find a spot 

 suitable to its growth, Nature has accomplished her purpose, and if 

 this one have reached a spot, perhaps hundreds of miles away, where no 

 corals previously existed, it founds a new colony, which possibly, 

 after the lapse of time, rises as an island out of the sea. These 

 embryos attach themselves to any firm point, but there is no instinct 

 leading them to select a favourable place ; Nature, therefore, produces 

 them in sucli countless numbers, that, on the theory of probability, 

 some are certain to obtain a suitable locality." 1 Who would deny that 

 this is precisely analogous to Helminths "losing their way ?" 



Moreover, von Siebold does not say of those Helminths that they 

 have wandered into the wrong host, but into the body of some animal 

 " not appointed to be their host." But this expression has really no de- 

 finite meaning. If a parasite develop in any given locality, we may 

 conclude that it finds there the necessary conditions of existence ; if it 

 do not develop, we may likewise conclude that the conditions are 

 unfavourable ; but who would undertake to decide whether or no a 

 particular host were " appointed ? " Von Siebold, however, goes still 

 further ; he states that these parasites which have lost their way do 

 not usually die, but continue to grow, " though, on account of the un- 

 favourable environment, they do not thrive, and fail to attain sexual 

 maturity," and in fact "degenerate." 2 Yon Siebold maintained this 

 opinion, 3 even after Ktichenmeister had endeavoured experimentally 

 to contradict it; 4 indeed his words at Konigsberg in 1860 show 

 that he was then still convinced of the accuracy of his opinion : " I 

 cannot understand why the possibility of degeneration in worms is 

 not admitted, since the same thing has been shown to take place in 

 higher animals, as a result of unusual conditions of climate and 

 changed food, and is regarded as a cause of the formation of new 

 species. If in many races an extraordinary growth of hair take place, 

 in some ruminants the horns become larger, the ears of certain domes- 

 tic animals become larger and droop, and in others again a local 

 deposition of fat takes place ; why is it not possible that in many lower 

 animals the influence of varying conditions of the body may give rise 

 to the presence of a serous fluid in certain parts, a local dropsy ? " 8 



1 JaJiresh. d. Ver. voted. Naturkunde Wiirttemberg, Bd. xvi., p. 31, 1860. 



2 Loc. cit. 



3 "Ueber Band- und Blasenwiirmer, u. s. w.," p.65. : Leipzig, 1854. 



4 Prager med. Vierteljnhrschrift, Jahrg. ix., p. 106, 1852 ; "Ueber die Cestoden im 

 Allgemeinen, u. s. w.," p. 12 : Zittau, 1853. 



6 " Konigsberg Naturf. Versamml.," 1860. 



