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Transactions of the Society. 
hairs distributed on one side of the shaft only. Another is a 
simple hair undivided (D), and there are several on the thorax, 
which will be referred to later. 
Most of these are in contact with nerve endings arising from 
the nerve and ganglia running along the ventral side ; others are 
in conjunction with a chordodontal or auditory organ, which occurs 
in each of several segments (A). This auditory organ com- 
mences ,as a simple nerve, in contact with one of the ganglia 
referred to ; it bifurcates, the two ends attaching themselves to the 
integument. It is, therefore, in a delicate state of tension, and in 
a position to register the sensation of any movement transmitted 
from the outside by hairs attached to the skin, but not directly 
connected with a nerve. 
One can readily appreciate that a Corethra — with a supply of 
sensitive hairs of various shapes attached to the integument and 
distributed over the body in positions mostly at right angles to 
the long axis of the body-hairs, which are so delicate and attenu- 
ated that it is difficult to make out their endings with a medium- 
power objective — is equipped to receive the finest impressions 
transmitted through the water of any moving object coming from 
any direction. 
We will now notice the three pairs of oval patches occurring on 
the thorax (fig. 6). Although we refer to them as patches, they 
are really bun-shaped or plano-convex, the flat side directed out- 
wards. These are generously supplied with strands of nerve 
tissue. On each of the patches are three long and elegantly- 
shaped compound hairs (fig. 7). We failed to find any reference 
to these in papers already published. 
Drawings were submitted to Mr. F. W. Edwards, and he gave 
it as his opinion that they were vestigial legs. He referred the 
matter to Dr. Kielen, who had worked out these vestigial legs on 
many dipterous larvae, and he confirmed this opinion, stating that 
he did not remember whether they had been noted before on this 
insect. Under polarized light the muscles of this larva show up 
most vividly. These oval patches remain unresponsive to this form 
of illumination, demonstrating that there cannot remain the slightest 
trace of muscular tissue ; the transformation, therefore, from a leg 
to some other organ is absolute. 
EXPLANATION OF PLATE XVI. 
Fig. 1. — Chaoborus crystallinus (De Geer) {Corethra plumicornis F.). 
Fig. 13. — Corethra pallida, head of. Zeiss 16 mm. ob. No. E.P. 
Fig. 14. — Corethra plumicornis , head thrown up, appendages displayed. 
Winkel 25 mm. No. E.P. Ilford panchro. plate, F. screen, x 28. Working 
aperture 0*17 ; exp. 30 sec. 
Fig. 15. — Normal position of the head. 
