24 
backwai’d into the posterior part hy the action of muscle libers which 
extend longitudinally between the inner surface of the outer sac 
and the base of the inner sac. The anterior part of the rostellum 
is thus telescoped, so to speak, into the posterior part (fig. 10). Both 
the outer and the inner sac are filled by a loose parench}"matous tissue; 
they are each supplied with longitudinal and circular fibers in imme- 
diate relation with their walls, besides numerous longitudinal fibers 
extending through the parenchjuiia. Zograf (1893) considers the mass 
of the rostellum to be made up of fibers running in a spiral direction. 
Mingazzini (1899) does not find any circular fibers, but considers 
longitudinal fibers only to be present, the relations of which are 
changed in difi'erent states of protraction or retraction of the rostel- 
lum so that they^ sometimes present the appearance of circular or 
spiral fibers. Xumerous muscle fibers also extend in yarious directions 
from the outer sac through the head. The size and relatiye dimen- 
sions of the rostellum are, natural!}^, somewhat variable. Leuckart 
(1886a, p. 997) giyes its size as 100 long by 88 yn wide. According 
to Blanchard (1891a) it measures 100 yn long b}^ 80 to 95 yn wide. 
iMiura & Yamazaki (1897) find it 56 // long, and Mertens (1892) giyes 
its size in the retracted state as 130 to 140 long by 80 yn wide. Meas- 
urements made in this laboratory of two specimens, in one of which 
the rostellum was protruded, in the other retracted, are as follows: 
First specimen, protruded portion of rostellum, 48 yn long by 60 yw 
wide; remainder of rostellum 100 yu long b}^ 80 yn wide. Second 
specimen, rostellum, 124 yn long by 60 f-i Avide; protrusible portion, 
50 yn long by 40 yn wide. 
NERyous SYSTEM. — Two main lateral longitudinal nerves^ one on 
either side, may be distinguished running through the entire strobila 
and united in the scolex b}^ a ganglionic commissure posterior of the 
rostellum. As Mingazzini (1899) noticed, there are sometimes appar- 
ent in the posterior third of the rostellum two masses of cells, one on 
either side. These cells are eyidently nerve cells and are similar to 
those found in the same situation in II. diniinuta and II. carioca 
(Zschokke, 1889; Ransom, 1902). The position of the lateral neryesin 
the segment is the usual one among the Taeniidag, namely, a short dis- 
tance laterad from the excretory yessels {m. 1. 7^., figs. 32, 33). 
Muscular system. — The muscular system is only weakly deyeloped. 
Beneath the cuticula lie the usual suhcuticular imiscular fibers — an outer 
circular and an inner longitudincd layer. 
The main part of the muscular system consists of a layer of longi- 
tudinal jibers lying in the parenchyma, not far removed from the 
cuticula and separating the segment into a central and a cortical 
portion. 
Linstow (1896a) maintains that in Ilymenolepis nana from man 
(fig. 32) the cortical portion is, in respect to the thickness of the seg- 
