48 WILLIAM A. HASWELL. 
simplest form (in the pharynx of a species of Syllis) the 
compound striated fibre has only a single transverse network 
running through a zone of singly refracting substance situated 
at about the middle of the fibre, with two doubly refracting 
zones, one on either sideof it. In a slightly higher stage two 
other transverse networks are added, one on either side of the 
middle one; in other species of Syllis the fibres present 
from half a dozen to twenty transverse networks. In the species 
(Syllis corruscans), in which the fibres are most highly 
developed, they have all the essential characteristics of the- 
striated fibres of the Arthropoda, differing only in the greater 
coarseness of the fibrils and of the networks. The develop- 
ment of the primitively simple transverse network from intra- 
nuclear filaments of adjacent intrinsic nuclei of the non-striated 
fibres is rendered probable by the correspondence of the trans- 
verse band of nuclei with the transverse network, and the 
replacement of the former by the latter. 
EXPLANATION OF PLATES IV & V, 
Illustrating Mr. William A. Haswell’s paper, ‘A Comparative 
Study of Striated Muscle.” 
PLATE IV. 
Fic. 1.—Isolated compound striated fibre from the “ gizzard” of Syllis 
corruscans, treated with bichromate of potash and stained with Heiden- 
hain’s hematoxylin. x 50. The longitudinal fissure renders visible the core 
of the fibre, with the nuclei of the ganglion-cell and the fine network of the 
core. 
Fic. 2.—A similar fibre, viewed from the anterior or posterior side. 
Fic. 3.—A fibre of the same tissue, treated with chloride of gold, formic - 
acid, and glycerine, under the same magnifying power as the last, showing the 
increase of dimensions and swelling of the muscle-substance due to the mode 
of treatment. 
