Physiology of litem atopinus tenuirostris, Burm. 101 



0*340 millim., and their least 0059 millim. ; their greatest 

 width 0-066, and their least 0"001 millim. 



Musculature of the Head. — The muscles of the head divide 

 into three groups : — those of the buccal organs ; the motors of 

 the antenna; and the motors of the head itself. 



Muscles of the Buccal Organs. — Of these there are two 

 kinds. Those which serve for the protrusion of the sucking- 

 tube are inserted upon the dorsal integument of the head in 

 the vicinity of the middle line and at the level of the antennae, 

 and pass thence, running obliquely forward, to the chitinous 

 bands which exist on each side of the proboscis. There are 

 four of them on each side (fig. 4 e & tig. 9 e) . Their mode 

 of action has been already explained (p. 87). The second 

 group comprises those which effect the retraction of the suck- 

 ing-tube. They originate on the ventral surface at the base 

 of the head, at a small distance from the middle line, two on 

 each side, and converging anteriorly, accompany the oesopha- 

 gus, pass between the antennae, and reach the sucking-tube 

 in front of them. These are fine and exceedingly long mus- 

 cles (fig. 4 y i). Their function has been already mentioned. 



Muscles of the Antennce. — Below the muscles which serve 

 for the protrusion of the rostrum two muscles originate on 

 each side at the dorsal surface of the head ; and these run 

 parallel to the above mentioned and go to the antennae. The 

 two muscles of each side lie close together, and only separate 

 a little before reaching the antennae. One of them goe3 to 

 the anterior, and the other to the posterior margin of the first 

 antennal joint ; the former is the forward and upward motor, 

 the latter the backward and downward motor (fig. 4, a). The 

 first antennal joint exhibits four muscles, two of which are 

 inserted at the anterior and two at the posterior end of the 

 base of this joint. These muscular bundles run converging 

 upwards to the lower margin of the second joint. In each of 

 the second, third, and fourth joints we see two muscles. They 

 originate at the base of the joint in which they are situated, 

 run parallel to the longitudinal axis of the joint, and pass to 

 the basal part of the succeeding joint. The fifth joint also 

 has two muscles, which run together above, and probably are 

 destined to move the tactile bacilli. 



To the third group I refer all the rest of the muscles con- 

 tained in the lower part of the head. 



Immediately below the point of origin of the muscles 

 which go to the antennae, and in part coincident with them, 

 there goes off on each side a muscular fasciculus to the right 

 and left (fig. 4, c). These muscles run from the dorsal surface 

 of the head towards the ventral surface. By their contraction 



