BY WILLIAM A. HASWELL. 
1709 
being, I presume, the interval between successive turns of the 
spiral. When a specimen of the tissue in question, which has 
been hardened in alcohol and afterwards stained by means of 
Heidenhain’s hjematoxylin method, is crushed, either in oil of 
cloves or in glycerine, by a series of blows on the cover-glass, the 
fibres tend to break up into fragments. In a considerable measure 
this breaking-up is longitudinal — the fibre being thereby split into a 
number of fibrillse. These fibrillse nearly all exhibit the striation 
described above ; but certain of them in the axis of the fibre do 
not show it — being apparently composed of a homogeneous sub- 
stance. Besides this division into fibrils the fibi’es exhibit in very 
many places a form of breaking-up which may be described as a 
peeling-off of the superficial layer. The cortical layer becomes 
split longitudinally and separates off from the rest, often becoming 
spread out into a broad ribbon. In parts where this occurs the 
broad and narrow bands can be seen to greater advantage than in 
the entire fibre, and a careful examination shows that this cortical 
layer is not composed of spirally wound fibrillar substance ; but is 
a continuous layer divided into regular tran.sverse, or more fre- 
quently, oblique, layers of staiuable and unstainable material.* 
As first noticed by Hancock f the posterior occlusor muscles of 
Waldheimia Jtavescens consist of striated fibres. These are very 
similar to the striated fibres of Lima just described, and the 
marking is apparently due to the same cause. The striation is 
readily visible in the case of specimens preserved by means of 
corrosive sublimate and alcohol, or alcohol alone ; but the stria- 
tions become much more distinct after the employment of Heiden- 
hain’s hsematoxylin ; I have not had the opportunity of examining 
fresh specimens. 
Simple striated fibres occur also in the Bryozoa, in which class 
they were described by Allman f in the case of the retractors of 
* Since the above was written I see from an abstract in the ‘ Journal of 
the Royal Micro.scopical Society ’ (October, 1888) that Fol has withdrawn 
his statement in so far as Fecten and Lima are concerned. 
+ “ On the organization of the liracliiopoda.” ‘ Phil. Trans.’ 1858. 
t “ A Monograph of the Fresh-water Polyzoa.’’ ‘Ray Society,’ 1856. 
