32 WILLIAM A. HASWELL. 
series being doubly refracting and readily affected by hema- 
toxylin or carmine (anisotropous segments) ; while those of 
the other set are singly refracting and are not readily stained 
(isotropous segments). 
3. Running transversely across the whole fibre in the middle 
of each singly refracting segment is a network or membrane, 
the transverse network, or Krause’s membrane. 
4. Running between the fibrils are a number of delicate 
threads, for the most part longitudinal in direction, consti- 
tuting the longitudinal networks. 
5. Each fibre is, so far as known, formed originally from a 
single formative cell, the nucleus of which undergoes division, 
giving rise to a multinucleated protoplasmic body! by modifica- 
tion of whose protoplasm the muscle substance and networks 
are formed. 
Now we find described as striated in many instances muscular 
fibres which want some of these characteristicsof striated muscle 
as seen in the Arthropoda and Vertebrata without the essential 
differences between the two sets of elements being noticed, 
the fact of transverse striation being regarded as the one 
essential point to be determined in classing the muscle. 
There are, in fact, to be recognised and distinguished two 
principal types of striated fibres, which may be termed the 
simple type and the compound type. I propose in the present 
paper to deal only with the latter of those two types, reserving 
the simple fibres for treatment in aseparate paper. The latter 
have, for the most part, only a single nucleus, and differ from 
the non-striated fibres of the same animal only in their 
substance presenting transverse markings. These transverse 
markings in the muscle substance are due in different instances 
to widely different peculiarities of structure. In no Case is 
there any evidence that they depend on the presence of trans- 
verse networks similar to those of the compound fibres. 
1 Remak, Lebert, Kolliker, Wilson Fox. 
