290 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The typical parts of the apparatus are the manubria, unci, fulcrum, and rami, 
and in our account of the variations of the trophi among different species we shall 
take onty these into consideration. 
In the small group of related species comprising Rattulus multicrinis Ivellicott, 
R. capucinus Wierz. & Zach., R. cylindricus Imhof, and R. latus Jennings, the 
trophi are nearly or quite symmetrical. The manubria are approximately of the 
same length and the alulte seem not strongly developed. 
Most of t he remaining species of the genus Rattulus have the trophi moderately 
unsymmetrical, the left manubrium being considerably larger than the right. This 
is the case, for example, in R. elongatus Gosse (pi. xii, fig. 107), R. longiseta Schrank 
(pi. viii, fig. 72), R. bicuspes Pell (pi. vm, fig. 70), and R. bicristatus Gosse (pi. ix, fig. 
80). In R. mucosus Stokes (pi. x, fig. 91) there is a much greater asymmetry, and 
the trophi have a very peculiar character. The left manubrium and uncus, the 
fulcrum and rami, are heavy and massive, while the right manubrium and uncus 
are reduced to mere slender rods. There appear to be no teeth, the trophi seeming 
to be designed rather for crushing than biting. 
In Diurella the asymmetry of the trophi is on the whole much more pronounced 
than in Rattulus , most of the species of Diurella. having jaws fully as unsymmetrical 
as those last described, or even more so. In Diurella porcellus Gosse (pi. n, fig. 22) 
the right manubrium is as long as the left, but is excessively slender — a mere bristle. 
In D. sulcata Jennings (pi. ii, fig. 2G) and D. tenuior Gosse (pi. I, fig. 10) the reduc- 
tion of the right manubrium has gone still farther ; it has become much shorter than 
the left one. In D. tigris Muller (pi. I, fig. 2), finally, the culmination of asymmetry 
is reached; the right malleus is a minute rudiment, while the left one is massive. 
Gosse (185G) described Diurella porcellus as having the right manubrium quite 
lacking. This is not the case with the specimens of that species which I have 
examined, though it is much reduced. I have found none of the Rattulidce in which 
the right manubrium could not be discovered. 
It is striking that the trophi are most unsymmetrical as a rule in the species of 
the genus Diurella, though the toes in this genus are less unsymmetrical than in 
Rattulus. This is probably due to the fact that in Diurella the body is as a rule more 
slender and more curved than in Rattulus. As the curve is of such a nature that 
the right side is concave, there is much less space on this side than on the convex 
left side, so the internal structures on the right side are reduced. This is especially 
noticeable in the trophi. In Rattulus, where the body is usually more swollen and 
less curved, there is not so much occasion for the reduction of the right side. 
(Esophagus. — The oesophagus is merely a short, slender passageway with thin 
walls, which begins on the dorsal side of the raastax, on its anterior one-fourth. It 
is well shown in fig. 63 (pi. vil), fig. 77 (pi. ix), and fig. 105 (pi. xii). 
Stomach. — The stomach is an enlarged sac, with thick, apparently glandular 
walls, forming a direct continuation of the oesophagus. In the broad-bodied species, 
such as Rattulus latus Jennings (pi. vn, fig. Go), it lies on the right side. 
At the anterior end of the stomach are the two gastric glands, one on each side. 
These are small solid structures, often lobulated and showing a number of prominent 
nuclei. They are well shown in fig. 77 (pi. ix), fig. 87 (pi. x), and fig. 102 (pi. xii). 
Intestine. — The stomach narrows at its posterior end to form the intestine (in., 
pi . vil, fig. 63 ; pi. xii, fig. 102). The walls of the intestine are usually thinner and less 
