M. Ivoidzumi 
247 
of the body. The flagella are directed backwards, applied more or less closely 
on the body wall, and are regularly arranged, so that they give the surface 
of the body a very beautiful appearance of parallel stripes. • 
The nipple is a very complicated structure (PI. X, fig. 13). It has the shape 
of a cone with an evenly rounded top, and rests on the anterior border of the 
bell. Its height is about 10 p and its width is about two-thirds of the height. 
It is remarkably rigid in consistency, so that it hardly shows any change of 
shape, even when the anterior portion of the body is swung actively in all 
directions. Four parts can be distinguished in the nipple, which were named 
by Porter as follows: (1) the axial rod; (2) the inner layer; and (3) the outer 
layer, surrounding the axial rod; and (4) the "cap at the top of the nipple. 
I propose to follow the above terminology, altering only '‘axial rod” into 
“axial core.” Of the above four parts, the axial core and the inner layer 
come together so as to form the axis of the nipple. The inner layer encircles 
the greater part of the axial core, leaving uncovered only a small portion of 
the apical part, which expands into a knob-like enlargement. The columnar 
part of the axial core is of almost uniform width, but slightly narrowed towards 
the anterior end, and having a constriction behind the knob. The knob and 
the constricted portion are quite structureless and refractive; while the 
columnar part is not homogeneous, but consists of two parts, namely, an 
outer wall of almost uniform thickness, and its contents—the latter appearing 
slightly granular and being continuous behind with the endoplasm of the bell. 
The inner layer is homogeneous in structure and refringent. The outer layer 
covers the inner layer throughout its whole extent. It is widest at the base, 
and is there about twice as thick as the inner layer. It gradually decreases in 
thickness towards the front end, where it becomes very much tapered and 
terminates under the knob of the axial core, together with the inner layer. 
Thus the above three parts assume anteriorly, as a whole, the shape of a dome 
with a knob resting on its top. 
The “cap” is a structure with the shape of a hemispherical bowl; it 
occupies the top of the nipple, with its margin resting on the sloping surface 
of the outer layer. The space confined by the cap in front of the above 
described dome-shaped part is filled with a homogeneous substance. I his 
part of the nipple is very rigid in this variety, and displays no recognizable 
alterations of shape. The outer layer is traversed by the fine flagella, which 
reach as far as the outer surface of the inner layer. The flagella are so 
numerous and densely set, that, both in top view as well as in side view, they 
appear to occupy the greater part of the outer layer. The most anterior 
flagella pass downwards along the sloped surface of the frontal part of this 
layer, and become free at the place where the margin of the cap rests upon it. 
The flagella are not of uniform length. Those situated at the tip are the 
shortest, and are nearly as long as the nipple. They gradually increase in 
length towards the base of the nipple, where they become twice as long as 
the height of the latter. 
