520 
HENRY LESLIE OSBORN 
suits. The sections are over-stained and the color is drawn 
under low magnification and can thus be checked very satis- 
factorily. 
EXTERNAL FEATURES 
This is one of the smallest distomes. Eighteen specimens, after 
mounting in balsam, show a variation in length ranging between 
0. 525 mm. and 1.3 mm. The length of four other micro-trema- 
todes is stated to be : Gymnophallus somateria 0.5 mm. (Odhner 
'00), Levinsenia pygmaea from 0.42 to 0.60 mm. (Jagerskjold 
'00), Distomom confusum and D. perlatum 1.3 mm. (Looss 
'94). The shape of the body, seen by a comparison of figs. 
1, 2, 3, and 4, is somewhat tubular, the anterior third is some- 
what flattened and the rest cylindrical. In the anterior level the 
diameters of the body are 0.155 mm. and 0.09 mm. Posteriorly 
the body is slightly compressed, measuring 0.15 mm. by 0.13 mm. 
(fig. 3). The enlarged proportion of the body in the middle 
region is easily seen to be directly correlated with the locations 
of the members of the reproductive apparatus. 
The oral sucker is very large and prominent relatively to the 
total size and much larger than the ventral suckers. It nearly 
fills the anterior end of the body and its length is contained about 
five times in the total body length. 
In most cases its outline has the form shown in figs. 1, 2 and 3. 
It measures .014 mm. by 0.12 mm. Its cavity is subdivided by a 
constriction near the centre which shows distinctly both in total 
preparations and sections (see fig. 3). The wall of the anterior 
part of this cavity is sometimes widely opened giving the sucker a 
very flaring funnel shape. A small percentage of my preparations 
have the oral sucker in this shape but the shape in fig. 1 seems to 
be the resting form of the organ. 
In the position usually occupied by the ventral sucker there is an 
adhesion apparatus which involves several features entirely 
unlike anything thus far known elsewhere among trematodes. It 
consists of a chamber with a mouth opening controlled by a 
sphincter muscle (6 in fig. 3). Located in this chamber there 
