284 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
the foot on the left side, hut not on the right. The foot is thus attached to the loriea 
in such a way that it can bend to the right, but not to the left. 
(4) Toes . — The toes form perhaps the most peculiar characteristic of the 
Rattul idee . Most- of the Rotifera have two short posterior appendages attached to the 
foot, placed side by side, and, like most paired organs, similar in form and size. 
But in the Rattulidce we find the two toes in the majority of cases unequal, 
sometimes excessively so, and no longer side by side. In some species one of the 
toes has almost disappeared, while the other has become immensely developed, 
forming a straight rod as long as the body, (in Rattulus cylindricvs Imhof, for 
example, pi. vii, fig. 62). 
Fig. 1 . — Dorsal views of the toes in a number of species of Rattulidae, showing gradual reduction of the right toe. 
(a) Diurella tigris Muller; (6) D. stylata Eyferth; (c) I), brachyura Gosse; (ft) I>. porcellus Gosse; (e) D. insignis 
Herrick; (/) D. tenuior Gosse; (g) Rattulus gracilis Tessin; (h ) R. lophoessus Gosse; (/) R. el ongatus Gosse. 
The steps in the series of changes by which this is brought about may be clearly 
followed by comparing the toes of different species. In a few species ( Diurella 
tigris Muller, D. sulcata Jennings, D. intermedia Stenroos, etc.) the two toes are 
still equal, as in other rotifers. One of these will serve best as a starting-point. 
We will select Diurella tigris Muller, whose toes are shown in text-figure 1, at a. 
'The toes form two long, curved, pointed, spine-like rods of equal size. At the 
base of each are four small flattened spines (so-called substyles), which usually lie 
closely applied to the base of the toes. The use of these substyles was pointed out 
by Plate (1886), and will be readily appreciated when one of the habits of the 
animals is understood. The posterior part of the body contains two large glands 
(pi. I, figs. 3, 4, m. r/.), which secrete a quantity of mucus, which is stored up in 
