W. H. Leigh-Sharpe 
3 
muscular rim (Fig. 1 r.) which grips the anal papilla of the host like an 
elastic band. From the rim to the mouth, in the hollow of the crater 
pass five muscular bands, arranged in the circle at equal distances from 
one another; these muscles, when they contract, no doubt bring the 
mouth of the leech into contact with the anus of the host, and perhaps 
indirectly increase the pressure of the muscles of the rim. The mouth 
is sht-like (not circular), the single muscle band being on the dorsal side, 
whilst two bands are lateral and two are ventro-lateral. It was observed 
mb. 
Fig. 1. Ganymedes cratere. The anterior sucker in frontal aspect, with the dorsal side 
to the top of the diagram, m,. mouth; m.h. five muscle bands; r. muscular rim. 
by the collector that the leech was attached to the anal papilla of the 
fish in such a way that the dorsal side of the sucker was towards the right 
side of the host. The leech, which, when the host is at rest, I presume, 
hangs vertically downwards, is therefore dragged through the water on 
its side, and cuts the water with the narrow edge of its abdomen. The 
shortness of the leech’s neck, however, will prevent its being bent far 
in a backward direction. 
The large size of the anterior sucker is explained by the facts: 
(1) that the leech by means of the muscular rim gives rise to an abnormal 
anal papilla on the host to which it remains permanently attached, and 
(2) that the sucker may act as a food reservoir, if the host’s faeces are 
discharged in greater quantity than the leech can immediately ingest, 
i.e. supposing the leech to be a faecal feeder. 
The suckers are only a shade paler than the rest of the body. The 
posterior sucker is almost functionless, presumably from disuse, the 
depression therein being exceedingly shallow. Admitting that the leech, 
as I saw it,- was in a dying condition, yet it made no attempt to use 
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