Nov. 17, 1882.J 



♦ KNOWLEDGE • 



4U1 



octagonal in shape, and was twisted through about a 

 sixteenth of a circumference, from the east towards the 

 north. For upwards of ten years the steeple exliibited 

 this curious token of the energy of the earthquake of llSlC, 

 but it was afterwards repaired. 



In other parts of Scotland very remarkable etiects were 

 experienced during the occurrence of this earthquake. 

 Three arches built across an arm of the sea in Sutherland 

 were flung down. A man who was walking amongst the 

 mountains of Lochindorb " was first alarmed by a sudden 

 and tremendous noise of a rushing wind, which came 

 sweeping up the hills like a roar of water ; this was in- 

 stantly followed by a rumbling noise, and the ground was 

 sensibly heaved up and down under his feet." A similar 

 noise and motion were observed near Jlontrose by two 

 excise officers who were on the watch for smugglers. They 

 were lying down on the ground when the shock came, and 

 one of them leaping up exclaimed, " There they are ! I feel 

 the ground sliaking under their horses' feet ! " 



It is worthy of notice that only six days before this 

 remarkable earthquake Mount Vesuvius had been in 

 eruption. 



HAIR EELS. 



By Dr. Andrew Wilson, F.R.S.K, F.LS., &.c. 



SOME time ago a correspondent of Knowledge wrote 

 to the Editor that a large number of " hair eels " had 

 appeared in tiie ponds and ditches in his neighbourhood. 

 He remarked, in the course of his letter, that he " noticed 

 one hair eel struggling with a black-beetle (probably a 

 water-beetle), which was floating on the surface of the 

 water. In a short time the hair eel, which was quite 

 white, had freed itself, and sank to the bottom imme- 

 diately. Seeing the two ' insects ' struggling together, 

 recalled to my mind that I had somewhere read of these 

 eels being internal parasites of black-beetles and grass- 

 hoppers. It would be interesting," adds the writer of the 

 letter, " to know if this is really the case, and if not, where 

 the eels come from, and what becomes of them on the 

 approach of winter." As there are doubtless many readers 

 of Knowledge who feel curious concerning the biography 

 of the hair eels, I will endeavour to state the few plain 

 zoological facts in which tlieir history may be said to lie 

 comprised. 



The zoological position of the "hair eels" is perfectly 

 well ascertained. They are, in a sense, " worms " ; re- 

 moved, no doubt, from the area of the ordinary earth 

 worms, sea worms, and the like, but still related by many 

 ties of kinship to these familiar forms. There is a group 

 of " worms " known to naturalists as Xeinatelmia, a name 

 literally meaning "round-bodied worms." In this group 

 the hair eels find a home, and their rounded form separates 

 them from the tapeworms and flukes, which are denominated 

 " flat worms " {Pldti/elmin). Included in the round- 

 bodied section, we find such worms as the common internal 

 parasites of man and other animals. Such are the " thread 

 worms " (Oxyiiris), the " common round worms " {Ascaris), 

 the Trichiiiti found in diseased pork, the guinea worm, and 

 allied species. All of these forms dilier from the ordinary 

 worms in possessing no well-marked ringing or segmenta- 

 tion of their bodies. Very rarely do we find in them the 

 side-bristles and appendages we see so familiarly in the 

 sea-worms, and also, but somewhat modified, in the earth- 

 worms and their neighbours. Again, most of the " round 

 worms," like most of the " flat worms," are parasitic, either 

 during the whole of their lives (':;/. tapeworms, flukes, 

 thread-worms), or during a part of their existence. Under 



this latter category, the hair eels may be ranked, as we 

 shall presently observe. 



The " hair eels " are technically named Gordmcea, and 

 the Gordius aqualicnx is the scientific name of the common 

 species. The well known vinegar eels, which make their 

 appearance in vinegar, in decomposing paste, and in Uke 

 fluids, resemble them in form, but, of course, diflfer ma- 

 terially in size. There are se^•eral curious points connected 

 with the anatomy and habits of the " hair eels," which, 

 by the way, should be properly named " hair worms," of 

 course. Thus, in the first place, their digestive system is 

 of imperfect nature, and no posterior aperture exists to this 

 system, which, in fact, opens into the cavity of the body. 

 This disposition of the intestine is not unknown in other 

 groups of the animal series, and its occurrence would seem 

 to indicate that the functions of the digestive apparatus are 

 in some respects differently carried out from those of normal 

 forms. Then, secondly, there exists in the hair worms only 

 an imperfectly-developed system of " water-vessels," such as 

 we find well developed in allied worms. The use of these 

 vessels is still problematical, but their presence is highly 

 characteristic of both round and flat " worms." 



In respect of their habits, howe\er, the hair worms are 

 peculiar. That part of the correspondent's letter in which 

 he speaks of the hair worm struggling with the insect, 

 becomes highly interesting, inasmuch as it supplies a clue 

 to the real history of these curious animals. One of their 

 chief characteristics is that they inhabit the bodies of in- 

 sects during at least part of their existence. They are thus 

 partially " parasitic" in their habits. The life-history of a 

 hair worm, in fact, begins with its appearance when libe- 

 rated from the egg (produced by the parent form), as a 

 minute speck, swimming freely in fresh water. This 

 youthful worm is provided with a boring apparatus, in 

 the form of a kind of proboscis armed with hooklets. 

 In this respect it reminds us of the young tapeworm 

 itself, which is provided with a crown of hooks adapted 

 for boring. Thus armed, the young hair eel seeks an 

 insect host, and boring its way into the insect tissues, 

 there ensconces itself. Development now proceeds so 

 far, that within the insect's body we find a hair worm 

 which may far exceed its host in length. Sooner or later 

 development is completed, and the adult stage reached by 

 the appearance of the egg-producing or reproductive organs. 

 Tlie sexes in the hair eels are situated in diflerent indi- 

 viduals. When the period of egg-deposition arrives, tlie 

 worm seeks to leave the insect^body which lias sheltered it. 

 It was at this stage of the hair eel's career that our corre- 

 spondent beheld the worm ; and, passing from the insect's 

 body, the liberated hair worm once again finds itself in tlie 

 water. Here the work of laying the eggs proceeds apace. 

 The eggs appear to be deposited in long strings in tin- 

 water, and after the process of development has proceeded 

 sufficiently far, we behold the young embryos, with their 

 boring apparatus, ready to repeat the parental history. The 

 swarms of hair eels which appear in our ponds and brooks 

 in summer are the newly-liberated worms about to begin 

 the work of egg-laying. 



Such being the well-ascertained history of the "hair 

 eels," we can readily value at its true worth the supersti- 

 tion, not yet extinct, which maintains that they arise from 

 horse's hairs, which by some marvellous process of vivitica- 

 tion assume the likeness of the worms. Over and over 

 again, in newspapers and elsewhere, have I had to combat tliis 

 absurd belief. Frequentlj', persons who should have known 

 better have assured me that they have placed horse's hairs 

 in a stream, and in a few days or hours have seen hair 

 worms swarm therein. Such ingenuous minds do not see 

 the ;)0.v< Iwc ergo propter hoc fallacy in which they indulge. 



