478 WILLIAM A. HASWELL. 
in Syllis a, though without the same strongly-pronounced 
character. 
In Syllis y, when the organ is strongly stained with hzema- 
toxylin, teased, and treated with glacial acetic acid, the inter- 
fibrillar networks of Retzius! are very clearly visible (fig. 7), 
having the appearance of longitudinal rows of extremely fine 
granules between the fibrils, and of thicker transverse lines 
(Krause’s membranes, transverse networks of Retzius), usually 
two, but sometimes only one, in each bright zone. The fact 
that the transverse networks appear stained with the hema- 
toxylin while the longitudinal do not, would seem to point to 
some difference in the substance of which they are composed. 
In the dim zone there is to be seen a broad well-defined trans- 
verse band, which is much more darkly stained than the rest. 
In such a preparation the fibrils will frequently be seen, when 
broken across, to tend to split up longitudinally into a leash of 
fine fibrillules (fig. 8), which coincides with the appearance 
of longitudinal striz in the fibrils of Syllis a as described 
above. 
Hollow polynucleated fibres of striated muscle-substance, 
similar in essential character to those above described, are found 
in various Vertebrates as an embryonic condition of the solid 
fibres, and in certain Insects and Arachnids as a permanent 
form. Simple (mononucleated) hollow fibres are found not 
unfrequently in various classes of the Vermes, and in some 
instances their substance may be transversely striated; but the 
occurrence in that group of compound or polynucleated fibres 
with transverse striation of a marked type is now recorded, as 
far as I have been able to ascertain, for the first time.’ 
1 «Zur Kenntniss der quergestreiften Muskelfaser,” ‘ Biologische Unter- 
suchungen,’ 1881; abstract in Hofmann und Schwalbe’s ‘ Jahresbericht,’ 
1882. B. Melland, who seems to have entirely overlooked Retzius’s paper, 
arrives at similar concluisons regarding the interfibrillar substance by means 
of the same method (staining with chloride of gold). ‘Quart. Journ. Micr. 
Sci, xcix, p. 371 (1885). 
> By Hisig, who in the memoir cited above, describes radiating cylinders of 
muscular tissue as constituting the greater part of the wall of the organ, the 
special nature of this muscular tissue has been overlooked. 
