The Melophagus, or Sheep-Tick. 441 



Having briefly noticed the external structure of the Melo- 

 phagus, we shall be inclined to take a fresh specimen and 

 examine its internal anatomy; a little patient dissection will 

 give us two very interesting observations. First, with regard 

 to the alimentary canal (Fig. V). Opening the Melophagus 

 with dissecting scissors under water, the whole will float out, 

 and show the eesophagus, the convolutions of the intestine, the 

 salivary glands, hepatic vessels, and some internal appendages, 

 which, with a higher power, we must now observe. 



This requires nice management of the dissecting needles to 

 open the enlarged part of the rectum, on which are four small 

 dots called by Dufour " Les boutons chamus." They mark the 

 position of four internal papillee found in most of the Diptera, 

 but with a modification in the Melophagus. They are slightly 

 mentioned by Owen in his Lectures on Comparative Anatomy, 

 but no observation is particularly made of the Melophagus, in 

 which the papillae instead of being smooth are covered with 

 short spines. (Fig. VI.) 



These singular organs are supplied with a branch of tracheal 

 vessels and strong muscles ; they evidently work freely in the 

 interior of the rectum, and assist in the expulsion of fcecal 

 matter. Probably, as the Melophagus is eminently sedentary 

 in its habits, these additional spines act as whisks and brooms 

 to clear the way where the muscular contractions are less 

 powerful and frequent ; or they may act as rakes and sieves to 

 separate the passing atoms and assist in the function of ab- 

 sorption. 



The next point of interest is the very remarkable system of 

 reproduction, whereby these pupivarous flies are separated in 

 rank from all the other Diptera. They are neither oviparous or 

 viviparous. 



The female nourishes a single egg within her body, attached 

 to her by an umbilical cord, which egg, in its early stage, pos- 

 sesses two small spiracles situated at its base (Fig. VII. b), by 

 which air is conveyed to the pulpy substance within, from an 

 open aperture in the abdomen of its mother. As the pupa pro- 

 gresses, eighteen spiracles develope on the surface of the skin, 

 small dots covered apparently with a transparent membrane 

 until the hour of its expulsion, when each tiny window flies 

 open, and the innumerable coils of trachea expand and contract 

 under the rush of life-giving air. 



The pupa case is brown and hard, lies loosely amongst the 

 wool ; the shepherds call them " eggs," but they are really the 

 protecting case of a young Melophagus. At the anterior end 

 of the pupa is a slightly marked seam, indicating the aperture 

 by which the fly will come forth. In the Melophagus, as in the 

 common dung-fly (Scatophaga), I observe a very distinct ptili- 



