Dec. 16, 1881.] 



♦ KNOWLEDGE 



133 



he said), as genial and good-natured a man as one would 

 care to meet, and with a strong sense of right and Justice 

 outside betting, had learned somehow that ten liorses can 

 come in (apart from dead heats) in 3,C2f<,800 dillereut 

 ways. This curious piece of information soenitd to him an 

 admirable way of gaining money from the iue.vperienced. 

 So he began to wager about it, endeavouring — though, 

 as will be seen, he failed— tD win money by wagering 

 on a certainty. Unfortunately, he came early across a 

 man as cute as himself, and a shade cuter {a britjand 

 brigand et demi), vho wordetl the question on which 

 the wager turns, thus : " In how many ways can 

 ten liorses be placed ! " Of course, this is a very dif- 

 ferent thing. Only tlie first three horses can be placed, 

 and the sets of three which can be made out of ten 

 horses number only 10 times 9 times 8, or 720 (there 

 are only 120 actual sets of three, but each set can be 

 placed in six diflVrent ways). My genial, but (whatever 

 he thought himself) not quite honest friend, submitted 

 the matter to me. Not noticing, at first, the technical use 

 of the word " placed," I told him there were 3,628,800 

 different arrangements, he rejoiced as though the money 

 wagered were already in his pocket. ^Vhen this was 

 corrected, and I told him his opponent had certainly won, 

 as the question would be undei-stood by betting men, he was 

 at first depressed : but presently recovering, he said, " Ah, 

 well ; I shall win more out of this little trick, now I see 

 through it, than I lose this time." 



I shall hereafter give some illustrations of the true prin- 

 ciples on which all chance questions shoidd be determined. 

 There is no hope that men general!}' wiD give up gambling, 

 but it is, at any rate, desii-able that when they gamble, the 

 chances should be as equal as they can be made ; that, in 

 iiict, they should not play (as the opponents of Lord Yar- 

 borough and my New Zealand fi-iend \\ere certainly playing) 

 against cogged dice or marked cards. The matter is one 

 strictly appertaining to tlie subjects with which Knowledge 

 claims to deal. There is science in chance, certainty in 

 probabilities. What is thus scientific and certain is what 

 we propose to bring before our readei-s. 



OUR UXBIDDEX GUESTS. 



Bv Dr. Akdrew Wilsox, F.R.S.E. 



' PHE fact that iu most animals there may reside, as 

 i "guests," within unconscious or unwilling "hosts,' 

 if-riain other animal forms, is, of course, widely known. 

 riiese animal "guests" form the "parasites" of the 

 natural historian. Bvit, although the fact of their existence 

 18 known, the general liistory of even the commonest para- 

 sites is a matter concerning which the general public are, 

 as a rule, lamentably ignorant. I say " lamentably," and 

 I mean what I say. A vast amount of disease, and that 

 of a preventible nature, is caused by the carelessness of 

 inan in the preparation of his food. This carelessness is in 

 *ts turn founded upon gross ignorance, for there are not a 

 few persons who believe that parasites come, like Dog- 

 berry's reading and writing, by nature, and that they 

 are part and parcel of an animal's constitution. That 

 this opinion is very far removed from the true state of 

 mattei-s can easily lie shown. It is perfectly provable that 

 animals were not created with the parasites infesting them 

 as we find them to-day. Common-sense forbids such a 

 supposition, and the organised common-sense we call 

 " science " shows us that the reverse is the case. All 

 parasites are acquired, and not original "guests." This 

 alone is provable by the facts of parasite-development. 



There is a bag-like parasite called SaccttHna, for instance, 

 which attaches itself to the bodies of hermit crabs. Nos\-, 

 sac-like though this parasite is, and destitute as it is of all 

 the ordinary belongings of animal life, it yet begins its 

 existence as a little free-swimming animal, exactly resem- 

 bling a water-llea. The first stages in a sacculina's 

 devolopment are, in sliort, like the beginnings of the 

 development of some shrimps, of barnacles, of water-fleas, 

 and of crabs themselves, though in a less marked degree. 

 Only after becoming degraded in structure does the sac- 

 culina become the " guest " of the crab. The mere facts 

 that sacculina is at first as free-living as a fish, and that it 

 afterwards settles down on the crali, testify, if we read 

 nature's story aright, that " once upon a time " the saccu- 

 lina race was not a parasitic one. Whether or not the 

 sacculina-stage itself Mas the beginning of the attached 

 existence, we do not know. It is most probable that the 

 bag-like body we term a " sacculina " was the result of the 

 adoption of the lower and rooted way of life. But, apart 

 from all other considerations, the main facts that a young 

 sacculina is always free, and tliat it begins life under a 

 similar guise even to some of the shrimp race, shows that 

 its parasitic life has been acquired, and is by no means an 

 original condition. 



Now the same rale holds good of all "parasites." The 

 development of most of them shows us the lingeruig 

 remnants of a once-free life. But there are other proofs 

 at hand of this assertion. There are degrees and stages in 

 the perfection of the parasitic state. There exist animals 

 which are mere "lodgers," so to speak — who "dine out," 

 but who repose within the anatomical establishment of a 

 "host." This is the case with certain little fishes, which 

 choose the very "jaws of the Hon " as a dwelling-place, 

 since they appear to live in the interior of certain big, 

 tropical sea-anemones. These fishes may be seen to swim 

 in and out of the anemone's mouth, and they may be 

 enclosed within the anemone's body when that animal 

 contracts itself, and yet swim free and unharmed out of 

 the mouth when these flower-like animals once more 

 resume their normal and expanded state. Here, then, 

 there is mere " association," but it is in some such associa- 

 tion that the beginnings of pure parasitism have orginated. 

 Suppose the case of an animal which, at first merely 

 " lodger," took to feeding upon the tit-bits secured by its 

 host for home-consumption. The " lodger," in such a case, 

 would practically become a " lioarder " as well. But 

 nature has a law as fixed as the edicts of the Medes and 

 Persians, called the "law of disuse." This law enacts that 

 whatever structures or organs of living beings are not 

 normally used, will waste and tend to disappear. It is the 

 operation of this law which has caused the two outer toes 

 of our horse to grow '■ small by degi-ees and beautifully 

 le^s," until they now appear as the " splint bones" on each 

 side of the single toe upon which the horse walks. And 

 ap2)Iying this law to the case of the animal lodger, we see 

 how an animal which does not require to move about 

 when resident within another animal will lose its organs 

 of motion. If it obtains fluid food, all ready digested, the 

 probabilities are its digestive system will become rudi- 

 mentary. Not requiring eyes or other sense-organs, these 

 will disappear ; and thus we see represented a kind of 

 zoological backsliding, which I'educes the parasite to the 

 elementary and degraded condition we, as a rule, discover 

 in the races of animal "guests." 



The histories of some of the most common parasites are 

 fraught with instruction, not to speak of the curiosity that 

 invests them. Take, for instance, the history of the fluke 

 {F(fsciola hepaiica), found in the bile-ducts of the li^er of the 

 sheep and ox. It is the presence of this parasite that makes 



