24 
backward into the posterior part by 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 parenchymatous tissue; 
they are each supplied with longitudinal and circular fibers in imme- 
diate relation with their walls, besides numerous lono-itudinal fibers 
extending through the parenchyma. Zograf (1S93) 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 various directions 
from the outer sac through the head. The size and relative dimen- 
sions of the rostellum are, naturally, somewhat variable. Leuckart 
(1886a, p. 997) gives its size as 100 long by 88 wide. According 
to Blanchard (1891a) it measures 100 j~i long by 80 to 95 ^ wide, 
^liura & Yamazaki (1897) find it 56 long, and Mertens (1892) gives 
its size in the retracted state as 130 to 140 /< long by 80 f.i 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 long by 60 yu 
wide; remainder of rostellum 100 long by 80 wide. Second 
specimen, rostellum, 124 long by 60 j-i wide; protrusible j^ortion, 
50 M long by 40 wide. 
Xervous system. — -Two main lateral longitudinal nerves^ one on 
either side, may be distinguished running through the entire strobila 
and united in the scolex by 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 evidently nerva cells and are similar to 
those found in the same situation in II. dirninuta and II. carioca 
(Zschokke, 1889; Ransom, 1902). The position of the lateral nerves in 
the segment is the usual one among the Taeniidae, namely, a short dis- 
tance laterad from the excretory vessels (// 2 . 1. ^., figs. 32, 33). 
Muscular system. — The muscular system is only weakly developed. 
Beneath the cuticula lie the usual suhcuticidar rnuscidar jihers—^n outer 
circular and an inner lerngitudincd la^^er. 
The main part cf the muscular system consists of a layer of longi- 
tudincd Jihers 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 Ilymenolejois nana from man 
(fig. 32) the cortical portion is. in respect to the thickness of the seg- 
