A COMPARATIVE STUDY OF STRIATED MUSCLE. 33 
Compound Striated Fibres. 
In these the fibre is derived from a protoplasm-particle the 
nucleus of which undergoes multiplication; the protoplasm 
subsequently becoming mainly converted into two kinds of 
substance, the general material of the fibres, which is usually 
regarded as being the contractile substance, and the material 
of the transverse and longitudinal networks. The former of 
those two sorts of material, the contractile substance, is 
probably derived from the more homogeneous and fluid part of 
the protoplasm of the formative cell—the hyaloplasm of 
Strasburger ; the latter from the lattice-work or network of 
less fluid threads—the spongioplasm of Leydig.! The former 
substance assumes two forms, differing in optical characters and 
in behaviour to staining agents like the two varieties of the 
substance in the simple striated fibre, and these two forms 
are arranged in alternating zones throughout the length of the 
fibre. The fibre is readily split up longitudinally into a number 
of narrower elements—the fibrils—the lines separating which 
are in some cases quite distinct in the living fibre. The longi- 
tudinal networks run between the fibrils, the direction of the 
threads being for the most part longitudinal, though there are 
numerous oblique strands and frequent anastomoses. The 
transverse networks, on the other hand, though they partly run 
in the interspaces between the fibrils, penetrate also, as will be 
shown subsequently, through the substance of the fibrils them- 
selves. There is a transverse network in the middle of each 
singly refracting segment, and by means of these the fibrils are 
placed in intimate connection throughout the whole length of 
the fibre. At the same time the transverse and longitudinal 
net-works are in perfect continuity. 
Compound striated fibres are only found in the Vertebrata, the 
Arthropoda, and certain Polycheta. The tissue presentsnumerous 
varieties, mainly dependent on differences (1) in the number 
of fibrils in a fibre, (2) in the number, closeness, and fineness 
of the transverse networks, (3) in the amount of indifferentiated 
' « Altes und Neues tiber Zellen und Geweben,” ‘ Zool. Anz.,’ 1888. 
