Bo2jal Microscopical Society. 267 



III. — On the so-called SueJiers of Dijtiscus and the Fidvilli of 



Insects. By B. T. Lowne, M.E.C.S. 



{Read before the Royal Microscopical Society, May 3, 1871.) 



The anterior pair of feet, in the males of the Genus Dytiscus and 

 its allies, are remarkable for their widely-dilatecl tarsi. These are 

 well kno^YU to microscoi^ists on accoimt of the sucker-Hke disks 

 with which their nnder surfaces are furnished. The middle pair of 

 tarsi, in these insects, are also furnished with disks on all then- joints, 

 in the males only. The function of the disks in both cases is to 

 assist the male during the act of sexual union. They are entirely 

 absent in the female. 



The disks are nothing more than remarkably-developed pulvilli, 

 although their adhesive power is usually attributed to atmospheric 

 j)ressnre; hence they are frequently spoken of as the suckers of 

 Dytiscus. 



The simplest form of pulvillus is seen on the tarsus of some 

 plant-loving beetles, and especially amongst weevils. I have 

 selected the beautiful foot-pad of the Australian diamond beetle as 

 an example. 



The imder side of the tarsus of this insect is densely clothed 

 with a velvet-like pile of golden yellow hairs. Fig. 11 represents 

 two of these hairs seen with a quarter-inch objective and C eye- 

 piece by Pioss. They are seen to be tubular, with shghtly bulbous 

 extremities. The wall of the bulb is thinner than the rest of the 

 hair. The bases of the hau's are connected with and open into a 

 large gland occupying the interior of the tarsus. This secretes 

 a viscid tenacious fluid which fills the cavity of the hair and exudes 

 through the walls of the bulb, thus enabhng the insect to obtain a 



EXPLANATION OF PLATE LXXXIX. 



Fig. 1. — The anterior tarsus of a male Dytiscus, with the integument of the upper 

 surface removed to show the gland wliich secretes a viscid Huid for 

 the supjily of tlie disks, a, tendon of claw ; h, main tracheal vessel 

 and sac. A portion of the sac is removed above to show the openings 

 into the disk-bearing hairs. 



„ 2. — One of the smaller suckers. 



„ 3. — Vertical section of the large sucker, a, c', a, under side of the tarsal joint 

 b, external elastic membrane; c, columella; c', opening into gland 

 (?, e, f, memljrane of disk ; g, chitinous cone in the centre of the disk 

 h, h, membrane of the gland. 



,, 4. — Disk of the large sucker; a, ovate space witliout radiating fibres. 



,, 5. — Internal orifice of the columella of the large sucker seen from the interior 

 of the gland. 



„ 6. — Transverse section of the disk of the same near the pedicle. 



., 7. — Section of the disk near the margin. 



„ 8. — A portion of tlie margin of the large sucker. 



„ 9. — Tuft from tlie same. 



,, 10. — Gland hairs from the foot of the }>lowfly. 



„ 11. — Gland hairs from the foot of the Australian diamond beetle. 



