ROTATORIA OF THE UNITED STATES. 
287 
(5) Corona. — The truncate anterior end is unprotected by the lorica and bears 
in the Rattulidai, as in other rotifers, cilia by means of which the organism moves 
and by which it obtains its food. Partly surrounded by the cilia are usually also a 
number of antenna-like organs. This whole complex of structures at the anterior 
end is known as the corona. In the Rattididce the structure of the corona does not 
vary a great deal in the different species. The main features of the corona will be 
seen by an examination of that of Diurella stylata Ey forth (pi. hi, fig. 31). Partly 
surrounding the corona, especially in the dorso-lateral region, are two curves of cilia 
(a), forming together nearly a semicircle. These two curves are not continuous 
with one another, but there is a gap between them in the middle dorsal region. 
These cilia are the organs of locomotion of the animal. 
At the sides of the mouth (m) are two other curves of shorter cilia ( b ). These 
are connected with food-taking, and may be said to belong strictly to the mastax 
or pharynx. When the mastax is pushed far beyond the surface of the head, as 
sometimes happens, these cilia are seen to be borne upon its end. This is well 
shown in fig. 50 (pi. vi), in Rattulus multicrinis Kellicott. 
In the dorsal part of the corona, in the median line, is a thick dorsal projection 
(pi. hi, tig. 31, c). In many Rattuliclce this is more slender than in Diurella stylata 
Eyferth. At the sides of this process, but lying a little ventral to it, are two smaller 
prominences (d) bearing cilia. Just above the dorsal projection, shown in fig. 31, 
is another thick dorsal process, shown in side view in fig. 27, e. 
The four curves of cilia described above (a and b) are present in all the Rattu- 
iSce There is also almost invariably a single, thick dorsal process (c). In the 
other antenna-like structures there is more variation. In Rattulus multicrinis 
Kellicott (pi. vi, fig. 57) the upper median process ( e ) is very long, while the lower 
one (c) is short. There are two long lateral processes (d) on each side. In Rattulus 
latus Jennings (pi. vii, fig. 65) the corona is similar to that of R. multicrinis Kelli- 
cott. The lower dorsal process (c) bears on its end two small processes. The parts 
of the corona which can be seen easily in most species of the Rattulidce are the cilia 
and the large dorsal process. The latter lies, as a rule, a little to the left of the end 
of the striated area of the lorica. 
The functions of the curious club-shaped or antenna-like organs of the corona are 
not known beyond the general probability that they are sense organs. 
In addition to the (probable) sense organs on the corona, there are three other 
structures which doubtless have sensory functions. These are the so-called dorsal 
and lateral antennae. 
Dorsal antenna. — The dorsal antenna is found, as in most rotifers, on the dorsal 
surface, some distance back of the anterior end of the head. It usually lies a very 
little behind the constriction which separates the head-sheath from the remainder 
of the lorica. It consists, in well-developed cases, of a small club-like structure, 
projecting through an opening in the lorica and bearing one or more fine setae. It 
is best developed in Rattulus cylindricus Imhof, where the seta which it bears is 
very long and conspicuous (pi. vn, figs. 62, 63, 64). 
From the antenna there may often be traced a fine cord running to the brain. 
This has, just within the lorica, a spindle-shaped thickening. 
In many species no setae can be observed on the dorsal antenna, and often the 
