182 PROF. T. MSKENNY HUGHES ON SOME TRACKS OF 
to more solid ground these strong sweeps, the rowing-legs, lift the 
body along ; so we see at the ends B and C of the specimen figured 
(Pl. VII. fig.1, 1a), that the mark produced by the body and walking- 
legs occurs only at intervals between distinct and well-defined im- 
pressions left by the ends of the long and strong swimming-legs as 
they are pressed into the mud at each stroke. 
Small animals which walk on their feet, such as Lithobius, ae ee 
Asellus, &e., produce tracks such as those shows eee fig. 1. 
When, however, they are moving through softer mud, the mark: 
produced by their feet become more a2¢ more obliterated, as seen 
in Pl. X. fig. 4, till we see only the ridges due to the sweep of 
their legs as they try to propel their body through the thick slime, - 
Pl) VILL. fig. 2, and (Pl. WX. fig.'4: gah requentiy turn round 
and round, producing a knot-like twist. Ke length they give it up 
and are smothered or wriggle away, leaving a DYE trail, like that 
of an earthworm. One such animal, which perished in the slush, I 
was able to preserve, still sticking at the end of the track 1¢ had 
made ; and this has been determined for me by Professor Westwood, 
of Oxford, to be a young specimen of Lithobius forepatus, Pl. IX. 
fig. 4. 
Any insect, even a large fly, sticking on the surface of the mud. 
in its efforts to get on, catches at the ground before it with its front 
feet, turning now rather to this side, now rather to that, in its 
attempts to get a grip, and makes the curious markings seen on PI. 
IX. fig. 2, which. somewhat resemble the appearance produced by a 
kind of alga on smooth rock-surfaces between high- and low-water 
mark. This kind of mark is also produced by the dipping point 
of a bending blade of grass moved by the wind; but in this last 
case the marks are somewhat less regular. 
I have noticed incidentally above, that earthworms and similar 
animals generally produce a smooth trail. The cross-barred tracks, 
such as those seen in Pl. X. fig. 4, are made by the larve of 
beetles &c., which move like caterpillars by shifting each body- 
ring in turn, whereas, when a worm has pushed the long anterior 
portion of its body forward far enough to get hold, as it were, it 
drags all the tail part after it by one continuous movement, so that 
the track is a smooth furrow ; where, however, there are no inequali- 
ties in the ground, and it is ‘too slimy for the worm to get a hold 
with its bristly rings, itis apt to follow a winding course, appa- 
rently in order to geta grip after the manner of a corkscrew. Some 
smaller creatures allied to earth-worms always do so, the fine 
wriggling track, Pl. X. fig. 4,is, I believe, made by Tubifex rwulorum 
or some such form ; but I have not been able to observe this 
accurately. 
Some of the most interesting tracks are those made by burrowing 
animals; and in connexion with them, I will notice several other 
phenomena related to them only by a deceptive similarity of form. 
There are three kinds of small pits or circular depressions 
common over all mud flats :— 
First, there are the impressions made by rain or hail, which 
