260 



KNOWLEDGE 



[No\'EMBEH, 1902. 



ii'ilucod. iiiul may ultiiiiaU'ly loso them altofjether. Siicli 

 ii sUigt} has, in liu-t, alroady boon reachod by one member 

 of the {,'1011]), whieli has thus lost all resemblance to a fly, 

 and, in fact, is popularly rej,'arded as hardly even an 

 insect, being called the .sheep-tick (Fig. 5). This name, 

 however, is a misnomer, as the true ticks are parasitic 

 tuites, eight-legged creatures belonging to the class 

 Arachnida, which includes spiders and scorpions. The 

 sheep-tick is six-legged, and is, of course, a true insect, 

 being, in fact, merely a much modified fly. Its scientific 

 name is Mehiphagus oriniis. It is a most repulsive-looking 

 creature of a dark brovn colour, about three-sixteenths of 

 an inch long, and is a common pest of sheep, to the fleece 

 of which it clings with extraordinary tenacity so as to be 

 diflicult to remove, while, at the same time, it is able 

 readily to vrork its way hither and thither amongst the 

 compact mass of hairs and so elude pursuit. It has 



Fig. 5. — Sheep-tick {Melophagus ovinus); a, claw of ditto, 

 mucb magnified. 



absolutely no wings, and at first sight it appears to have 

 uo head ; but this is because the head is completely sunk 

 in the thorax, so that there is uo constriction between the 

 two, nothing in the nature of a neck. In this feature it 

 departs very widely from the normal plan of fly structure. 

 The head of a fly is usually attached to the body by so 

 slight and narrow a junction, that it can be partially 

 revolved round its pivot from side to side, and a mere 

 jarring is sometimes enough to decapitate a dried speci- 

 men ; this the dipterist often finds out to his cost, for a 

 collection of flies, unless most carefully kept, is pretty 

 sure to suffer more or less loss from the accidental decapi- 

 tation of specimens. But uo such calamity could ever 

 befall a sheep -tick. 



As in all these " lou.se-flies," the abdomen looks like a 

 more or less flattened bag and shows no trace of segmenta- 

 tion, and its peculiar construction is associated with one 

 of the most remarkable characteristics of these in other 

 respects equally extraordinary creatures. There are 

 several members of the order Diptera, such as the flesh 

 flies for example, that retain their eggs long enough within 

 the parent's body for them to hatch, and hence the young 

 are produced in the foi-m of maggots. But this sheep- 

 tick, as well as the other louse-flies already described, 

 carries this peculiarity still further, and the birth of the 

 young is delayed, not merely till they cease to be eggs and 

 are hatched into maggots, but even until they have passed 

 through their whole larval life and are just on the point 

 of becoming pupaj. While within the maternal body these 

 larvae are nourished by a sort of milky secretion furnished 

 by the parent. The so-called eggs that the fly produces, 

 therefore, are not really eggs at all, but consist of what in 

 flies is called a " puparium," i.e., a case composed of the 

 last larval skin, containing within it the true pupa or 

 chrysalis. These pupse are of course very large, and one 

 of "them is enough to occupy all the available space in the 

 fly's body, and therefoi-e, necessarily, at each birth the 

 insect's progeny is restricted to a single individual. Of 

 course, the size of these so-called "eggs" would alone be 

 suflicient indication that when thus named they are mis- 



I'alled. From the peculiar method of their reproduction, 

 this particular gi'ou]) of flit's is sometimes called the 

 l'u]>ipara, or jmpa-producers. 



It might have been supposed that in the sheep-tick these 

 parasitic Dii)tera had reached the lowest de])th of degrada- 

 tion and achieved the maximum of modification, but such 

 is not the case; there are other species that exhibit a still 

 more modified and degraded form, and are thus still more 

 unlike what one ordinarily understands by the word " fly." 

 First there are the so-called Spider-flies or Bat-lice, 

 belonging to the genus Nyderihia. They are little 

 creatures, only about ^ of an inch long, of very active and 

 agile habits, living parasitically on bats. The head is 

 reduced to a rudimentary condition, and what little there 

 is left of it is sunk deeply in the thorax, so that the insect 

 appears to begin with its first pair of legs. They are quite 

 wingless and look more like small spidei-s than flies. Still 

 smaller, more rudimentary, and less fly-like is the little 

 Braula, or bee-louse, a parasite on bees. 



From what has been said above, it will incidentally have 

 become manifest that vei-tebrate animals are subject to 

 the attacks of at least six distinct sets of parasites of quite 

 different tyjies, the popular names for which are more or 

 less confused, and do not always truly represent the 

 zoological position of the animals, so that such words as 

 lice, ticks, &c., by themselves are but vague, and convey 

 little more distinct idea than that of parasitism. Best 

 known are the fleas, an aberrant group of dipterous insects, 

 and the bugs, belonging to the Hemiptera. Then there 

 are the tme lice, with suctorial mouth, which may perhaps 

 be regarded as degraded Hemiptera ; the true bird-lice, or 

 Mallophaga, with biting mouths ; the Pupipara, or so- 

 called spider-flies, bird-flies, bird-lice, bat-lice, or louse-flies, 

 a parasitic section of the Diptera ; and lastly the ticks, or 

 IxodidiK, which are not insects at all, but are allied to the 

 mites and spiders in the class Arachnida. Even these six 

 groups do not exhaust the list of those persecutors of 

 vertebrate animals that actually take up their residence 

 upon the bodies of their victims, though they are all that 

 happen to have occurred to us in our investigations 

 thus far. 



.o 





Conducted by M. I.Ceo§s, 



PoND-i.lFE C'oLLECTlNt; IN XcivEMHEU. — With the advent of 

 November, Pond-life all round becomes less abundant, and fewer 

 species are to be met with. By degrees many of the water- 

 plants die down, and the fauna is reduced to such forms as can 

 subsist throufjh the winter. Those animals which cannot do 

 this, such as Polyzoa, Uaphnia, some Rotifera, etc., have by this 

 time produced so-called winter eggs or resting germs. The 

 winter fauna, however, is much more numerous than is 

 usually assumed. Among Rotifers, several species of SijncliiTta, 

 S. pec'tiiiatd, trcmnla and ohUmga, seem to like the winter quite 

 iis well as the summer ; then tiic following maj' also be expected 

 in moderate numbers : .[njilanchna jtrindontd, Aiivraa aciileata, 

 Polyarthni plati/ptera, liotifer vulgaris, Euclilaiiis deriexa, 

 Triarthrd lonf/iseta, Bracliiomis aiigularis, Conochilus iinicoriiis, 

 Digh'iia J'oiri/niki, J)ia!icli/:a liicinuhila and ramphu/cra. Vino- 

 cliarix li'li-d' ti.s, and others. Among the Infusoria, the Vorticella 

 in particular seem to like the cold season, and a number of 

 different species, and often large colonies, can be found attached 



