348 
Transactions of the Society . 
Working back from the head, there are six pairs of valves 
situate between the two pairs of air sacs ; and it was only after 
prolonged observation, seeing a few of the scanty supply of 
corpuscles enter, and in no instance pass out of the open valves, 
we were satisfied they were intakes. 
A rhythmical pulsation takes place along the heart, counting 
from the tail end ; the first three pairs of valves open and close very 
briskly in a series of somewhat jerky motions. The remaining 
three pairs are sluggish — the opening and closing is just per- 
ceptible. During the process of contraction the valve remains 
closed, but springs open when expansion is almost complete, 
shutting immediately the maximum diameter of that portion of the 
heart has been reached. A regular sequence of opening and 
closing of the valves takes place as the pulsations travel along the 
vessel. At the eighth segment the heart develops into a sac much 
larger in diameter than any other part of the organ, the pulsation 
of which is very vigorous. It is here we find a very beautiful and 
interesting arrangement of delicate strands, which form an organ 
of attachment holding the sac in position, and no doubt assisting 
in its action. These strands are connected at various points to the 
sides of the sac, converging to a point where they become attached 
to the integument. 
In addition there are two other strands of more robust structure 
passing out from the entrance of the heart, and also attached to the 
integument. The rhythmical contraction and extension of these 
delicate threads, working in perfect harmony with the contraction 
and dilatation of the heart, is a sight well worth the time and care 
necessary in setting up the proper illumination and adjustment 
of the microscope to observe. 
The next point of interest is the two pairs of ganglia destined 
to control the valves and the pulsation of the dorsal vessel, one 
EXPLANATION OF PLATE XVII. 
Fig. 11 . — Corethra plumicornis, anal segment. Winkel 25 mm. obj. No. E.P. 
Ilford panchro., F. screen, x 36. Working aperture O’ 17 ; exp. 2 min. 
Fig. 12. — Naturally drawn down anal segment. Focus arranged to show 
detail of hooks extended. Two-thirds obj. No. E.P. Ilford panchro., F. screen. 
X 120. Working aperture 0*21 ; exp. 8 min. 
Fig. 16 . — Corethra pallida, anal segment. Zeiss 16 mm. obj. No. E.P. 
Fig. 18. — Lens behind granules forming eye spot of young larva. Swift Jjy in- 
O.I. obj. NA. 1-22 No. E.P. x 800. Exp. 20 min. 
Fig. 20. — Impression of a tube, or cord, round the periphery of the sac. This 
effect is produced by the formation of the hoops. Leitz 13 mm. NA. 40 Ilford 
panchro., F. screen, x 80. Working aperture 0*35; exp. 1 min. 
Fig. 28. — Banana-shaped pupal air tubes developed in the thorax of the larva 
before collapse of thoracic air sacs. Swift 2 in. No. E.P. Wratten panchro., F. 
screen, x 16. Working aperture 0 - 15 ; exp. 45 sec. 
