Mr. ClARkV Obfervat'ions on the Genus Oe/lrus. 293 



be obfeiTcd two fmall horny plates, which are found on diire61:ion 

 to clofe the extremities of the trunks of fome large air vefTels. 

 Near to thefe plates, and fomewhat above them, a minute puncture 

 is difcernible by the affiftance of a microfcope, which was firft de- 

 te6led by placing the /arva recently removed from the beafl: in warm 

 water, when a confiderable column of yellow pus was obferved to 

 rife from this aperture, which rendered it fufficiently vifible. At 

 other times, when clofed, it was difcernible with the utmoft diffi- 

 culty. At fig. 20, is reprefented this aperture (a), together with the 

 two horny plates, which clofe up the air veflels, being a view, very 

 confidcrably magnified, of the upper extremity of the larva fig. i. 



From a firft view, this part would appear to be the head of the 

 larva ; but as it is found to produce the extremity of the abdomen 

 in the future infedl, it muft be confidered as the tail; and the above- 

 mentioned minute aperture is undoubtedly the anus, and is found 

 to be in conformity to the fame fituation of the anus in others of 

 this genus. 



At the lower end of the larva, fig. i, a fmall indentation may, 

 with attention, be obferved, which is the mouth of the larva. It is 

 a fimple aperture, and altogether unprovided with any of the appa- 

 ratus belonging to the mouths of larva in general ; and near the 

 mouth are fecn two black points of horn, which appear to be per- 

 forated in the centre, and are found by diffeftiou to be the termi- 

 nation of two confiderable branches of the air tubes, and correfpond 

 to the two nipples on the laft fegment of the larva.oi the CE. Equi, 

 feen at fig. 22, a. An enlarged view of the mouth and inferior 

 part of the larva of the CE. Bovis is feen in fig. 21. Round the orifice 

 of the mouth are placed fome projefling mamilla, which arc im- 

 perforate, and perhaps fcrve the purpofe of feelers. 



The inteftinal canal in this lai'va is a fimple membranous tube, 

 2 which : 



