274 



HARDWICKE'S SCIENCE-GOSSIP. 



[Dec. 1, 1S63. 



THE SLUG PARASITE. 



Philoclromus Limacum. 



OUR worthy grandmothers, intent upon training 

 us up reverently in the paths of faith and virtue, 

 endeavoured to force upon our infant minds their 

 own unquestioning belief that the unclean vermin 

 which may not even be alluded to in polite society 

 were created by Providence solely as " a visitation " 

 upon wicked and dirty vagabonds. Even in this 

 present year of grace there are grannies (of both 

 sexes) who religiously maintain that the recent 

 cattle plague was " sent as a judgment " upon the 

 drovers and butcher-boys for using bad language 

 and sharp-pointed sticks to quicken the paces of the 

 tardi boves consigned to their tender mercies. Even 

 if the mission of the irritating legions was restricted 

 to tramps and beggar-wenches, I fear that we could 

 not accept this philosophy as final. 



Our eyes declare to us that there is scarce a living 

 thing, great or small, that is not pestered with 

 "hangers-on," harder to shake off than a poor 

 relation or a pious lady in quest of a subscription. 

 It is not only Lazarus on his dunghill, or the poor 

 Cockney at his cheap watering-place, who is almost 

 eaten up alive ; the whole creation scratches, or at 

 any rate itches and would like to scratch, but the 

 fingers and claws necessary for the due performance 

 of that vulgar operation do not happen to be univer- 

 sally distributed. Probably there is not an animal 

 (using the term in its widest sense) that enjoys 

 perfect immunity; the bullet-proof rhinoceros is 

 worried by a tick, and the great whale is often so 

 completely covered with suckers, barnacles, and lice 

 that his skin is invisible, and he bellows like a great 

 overgrown calf, while he rubs his blubbery sides 

 against the rocks. But it is not only the giants that 

 have toll levied on their vital juices : 



The little fleas that do so tease 

 Have smaller fleas that bite 'em, 



And these again have lesser fleas, 

 And so ad infinitum. 



Most of us I dare say are familiar with a small 

 member of the class Arachnida (Gamasus coleoptra- 

 torum) which infests the beetle, and is so large and 

 so like the insect it feeds upon that it is sometimes 

 popularly mistaken for its lawful progeny, only 

 wanting a little time to change colour and grow to 

 the size of its reputed parent. 



But here is a still humbler creeping thing, not 

 generally pleasant to contemplate, — indeed it almost 

 turns the stomach of Mrs. Grundy ; here is a com- 

 mon slug, Limax cinereus {vel maximus, vel varie- 

 gatus, vel maculatus, according to your choice : the 

 first is the name affixed to him by "Forbes and 

 Hanley.") I caught him only yesterday afternoon as 

 he sallied forth from a cool damp drainpipe to make 

 a raid on my melons — my very choicest musk-melons, 



whose parents grew in a bed of rich black volcanic 

 earth at the foot of Eusi-Yama. Angrily shovelling 

 him up on a broken pane of glass from the hot-bed, 

 I was about to consign him a bonne louche to the 

 ducks, when I perceived a dozen or so of little 

 yellow mites racing about with extraordinary ac- 

 tivity all over his slimy body ; and, thinking them 

 worth an hour's study, I disappointed the old mal- 

 lard, whose tail was already in a wiggle-waggle of 

 expectation, and deposited my slippery customer 

 with the many aliases on a plate under a bell-glass 

 in my sanctum sanctorum. 



Let us look at him for a minute as he glides 

 across the dome, presenting his ventral aspect to us. 

 He is stretched out to his full length, nearly five 

 inches, and is travelling at top speed; we cannot 

 say that he is putting his best leg foremost, for he 

 is guiltless of legs, but he is literally " pulling foot *» 

 as hard as he can, and his foot is indeed a wondrous 

 contrivance ; the strong hot glare of the sun, from 

 which he is so anxious to escape, shines through it, 

 rendering it almost transparent, so that we can see 

 the play of the thousand muscular bands with the 

 naked eye. At first we are almost tempted to fancy 

 that we see a broad canal in the mesian line of the 

 sole, containing a greenish fluid passing through a 

 series of valves and producing an undulating gaining 

 motion, and that progression is effected by this 

 hydro- dynamical apparatus. A novice might be ex- 

 cused for dreaming that he was witnessing the blood 

 flowing in rhythmic tide from the tail to the head ; 

 he sees no fluid in motion, but incessant muscular 

 contractions which present to his eyes a miniature 

 of the impression produced upon them by the rolling 

 billows of a green cornfield when a brisk breeze is 

 sweeping over it. 



Professor Owen, in one of his lectures on the 

 mollusca, says, " The cutaneous muscular layer 

 consists of oblique, longitudinal, and transverse 

 fibres, intimately united with the corium. Upon the 

 ventral surface it becomes very thick and forms a 

 long disc called ' the foot.' The fibres of this part 

 contract successively so as to form wrinkles or 

 transverse waves, following each other from behind 

 forwards, whereby the disc glides over solid bodies 

 or the surface of the water." 



Here are at least a dozen of these </>i\6c?po/zoi 

 disporting themselves on Limax's speckled sides ; 

 there they go for a short preliminary canter, and 

 now they dash off for a long heat. Reaumur was 

 of opinion that the viscid secretion destroyed these 

 parasites, but Nature never made such a blunder as 

 to ordain for one of her creatures a habitat that 

 must be fatal to it, or to neglect to adapt its 

 physical conformation to the peculiar conditions, no 

 matter how strange, under which it was designed to 

 exist. Lamark states most positively that he is 

 convinced that these acari are strictly parasites, 

 attached to the slug family, and are not mere casual 



