224 Transactions. — Zoology. 



the lower skin possess, immediately above the antennae, an 

 arcuated impression-line, which seems to separate from the 

 front a small, usually crescent-shaped piece termed the frontal 

 crescent {lunula frontalis) . When the eyes meet on the front 

 so as to divide it into two triangles the superior one is called 

 the vertical triangle (triangulum vcrticale), the inferior the 

 frontal triangle (trianguluvi frontale). The anterior portion 

 of the head, reaching from the antennae to the border of the 

 mouth or oral margin (^pcristomium) , is the face (fades). The 

 aiitennae are separated into two series of joints, the first con- 

 sisting of the two basal joints, called the joints of the scapus, 

 and the following those of the ftagellicm. Beneath the antennae 

 there are sometimes found longitudinal grooves {fovea antcn- 

 nalis) for their reception. The sides of the head from the eyes 

 downwards are called the cheeks {gence). A somewhat swollen 

 ring sometimes surrounds or partly encompasses the swollen 

 eyes, and is termed the orbit {orbita), the successive parts of 

 which are the anterior {orbita anterior sive facialis), inferior 

 {inferior s. genalis), posterior {posterior s. occiioitalis) , superior 

 {s^iperior s. verticalis), and frontal {frontalis) orbits. Where 

 no such ring is visible a distinct colour or some peculiar 

 structure marking the nearest surroundings of the eyes is 

 described on the orbit. The parts of the mouth {os) employed 

 for sucking are called the sucker or proboscis ; when attached 

 to a long and generally cylindrical projection of the head it is 

 called a snout {rostrum), and must be distinguished from a true 

 proboscis. They may project from a wdde aperture occupying 

 a great part of the under-surface of the head, called the mouth- 

 hole {cavitas oris). The common fleshy root of the oral parts 

 is connected by a membrane with the border of the mouth. 

 This membrane has a shield sometimes almost carneous ; it 

 is then termed the clypeus, or shield {clypjcus prcelabrum). It 

 is either entirely connected by the anterior border of the 

 mouth, aTid is then movable, or it projects over it as a ridge, 

 and it is then generally immovable. Generally the largest of 

 the mouth-parts is the fleshy underlip {labium or hypostoma), 

 made up of the stem {stipes) and the knob {capituluin labii), 

 formed of two suctorial flaps {labella). Close by are to be seen 

 the palpi, which are important to notice, being frequently very 

 characteristic. The tongue {lingua), upper jaws {^mandibula) , 

 lower jaws {maxillcB), and upper lip {labrum) are not only in- 

 conspicuous, but generally difflcult to recognise, and are rarely 

 of value in distinguishing species. According to Meinert, the 

 pharynx is separate from the first metamere, on which the 

 labium and labrum are situated ; on the second metamere the 

 maxillae and their palpi are placed ; while on the third are 

 situated the mandibles. 



