440 The Melophagus, or Sheep-Tick. 



The Melophagus (Fig. I.) is apterous, and possesses some 

 remarkable links with, insects of both, higher and lower organiza- 

 tion. It is easy to procure, and makes a good object, also 

 for the microscope, if soaked in potash, washed, dried, and 

 mounted in balsam, when it polarizes brilliantly. For present 

 examination we need but use a low power, and look at it as an 

 opaque object, observing that the coriaceous, bristly body is 

 divided as usual into three distinct parts — head, thorax, 

 abdomen ; but that, unlike the rest of the Muscidse, the 

 abdomen has no segments, because the system of reproduction, 

 differing entirely from the oviparous or viviparous flies, requires 

 an elasticity and firmness in that part which, could only be 

 obtained in a perfectly continuous substance ; yet, when the 

 female has expelled the pupa-form of her progeny, there is 

 found, more or less, in the Hippobosca, Ornithomyia, and 

 Stenopteryx, transverse plaits or folds of the abdomen answer- 

 ing perfectly to the segmentation of a dipterous abdomen, but 

 fading quite away in the Melophagus. 



We may also notice the comparatively few facets in the eye 

 of this sheep-tick, which, needs no more for its sedentary life 

 amidst the dark mazes of the matted wool ; a highly reticulated 

 eye, like that of its nearest relative, the Hippobosca, who darts 

 about in the sunshine, would be wasted here. 



The position and strength of its legs we observe as exactly 

 adapted for pushing through the woolly thicket, with claws like 

 harpoons, toothed and striated (Fig. VIII.) , clinging so despe- 

 rately to the sheep that desperate measures are needed to relieve 

 the animal of its parasite. These are only well seen in the 

 mounted specimen, and so also must we prepare the insect to 

 see the perfection of its suctorial apparatus. This is composed 

 of a pair of hairy valves protecting a very slender siphuncle, 

 rigid and sharp, and may be compared with that of the horse- 

 fly, which is shorter, because exercised upon the nearly naked 

 skin of the horse, whereas the Melophagus requires a long, 

 flexible dart, in searching for a vulnerable point amidst the 

 clotted wool. 



The next point of iuterest will bo the number, position, and 

 variation of its spiracles. 



It has nine pair of these breathing organs — two pair in the 

 thorax, seven in the abdomen (Fig. III.) — round in form, and 

 edged with simple cilia, quite unlike the* spiracles of the Mus- 

 cida) ; for as this insect passes its lifo in the suffocating atmo- 

 sphere of a woolly back, it wanted every facility for inhaling the 

 necessary oxygen, and therefore has many more spiracles, and of 

 much less complicated form than the house-fly and its brethren. 

 These circular spiracles dilate and contract, the cilia shorten by 

 a muscular contraction at their base, and leave a perfectly open 

 space. (Fig. III. a.) 



