THE SOLDIERLESS TERMITES OF AFRICA 9 



great variation in the length of the mesenteric overlap with the proctodeum, that is, 

 the mixed segment, and its position related to that of the malpighian tubules pro- 

 vides both generic and specific characters. The enteric valve has a highly variable 

 degree of armature and development and again provides both generic and specific 

 characters. Its attachment to the pouch of the posterior part of the hind gut 

 is modified in some genera by the development of part of the pouch into a tubular 

 neck terminating in a more or less bilobed or trilobed valve-seating. This is usually 

 visible through the body wall of an unopened worker termite, and its position is 

 determined by the length and coiling of the various parts of the gut. The position 

 of this structure can be stated relative to adjacent sternites or tergites and so 

 provides a further useful character (Text-fig. 6). In some species the 'lobes' of 

 the valve seating are developed into distinctive diverticula. Although some of 

 these features can often be seen through the body wall, it is usually better to sacrifice 

 a specimen to see them clearly. To examine the armature of the enteric valve a 

 dissection and slide preparation are essential. Finding these structures and dis- 

 secting them out is not always easy and a more detailed description of the gut is 

 needed. A diagram of dorsal and ventral views of a typical worker termite of this 

 group is given in Text-figs 4 & 5. In dorsal view the long oesophagus traverses 

 the narrow thoracic segments to open into the sac-like crop with the relatively 

 feebly developed gizzard at its distal end. This is found beneath the foremost 

 abdominal tergites and rests above and in front of one or two coils of the narrow 

 part of the hind-gut. The wide and thicker-walled mid-gut (mesenteron) leads 

 from the gizzard at first backwards on the left hand side in a loop round the outside 

 of the coil of hind-gut (proctodeum) passing forwards and downwards on the right 

 towards the ventral side. Viewed from the ventral side the mid-gut appears on 

 the left leading forwards and across the front of the abdomen, just behind the 

 posterior pair of legs. The loop of the gut passes across to the right, and the junction 

 with the hind-gut is found in this region. The thin-walled hind-gut passes down 

 the right hand side of the abdomen, and at the distal end crosses over to the left. 

 Here it narrows to enter the enteric valve or passes round to the left lateral or dorsal 

 side before reaching the valve, according to the proportions of the various parts 

 of the gut. The pouch of the proctodeum beyond the enteric valve leads forward 

 again to the coil within the mesenteric loop, and thence beneath this loop down the 

 dorsal side to the dilated rectum. The junction between mid- and hind-gut may be 

 simple, or overlapping as already stated to form a mixed segment of variable length. 

 The four malpighian tubules severally enter the inner side of the mid-gut on the left 

 in ventral view. They first loop backwards over the second pouch of the hind-gut 

 and then pass forwards over the mixed segment into a tangled knot, which often 

 extends into the distal part of the thorax under the hind coxae. This structure 

 will be referred to as the 'malpighian knot'. From the malpighian knot the tubules 

 spread out over the mid-gut and gradually become thinner to their ends, which 

 loop back over the mixed segment and other parts of the gut. The function of the 

 malpighian knot is unknown but it serves as a useful landmark in measuring the 

 development of the mixed segment and as a recognition feature for this group of 

 termites. No other group has the gut coiled in this precise way, which is thus 



