348 PROCEEDINGS OF SECTION D. 



13.— A COMPARATIVE STUDY OF STRIATED MUSCLE. 



By William A. Haswell, M.A., D.Sc, Lecturer on 

 Biology, University of Sydney. 



[Abstract.'\ 



A CONSIDERABLE proportion of the discrepancies to be observed 

 between the statements of difierent authors as to the distribution 

 of striated muscle are to be ascribed to a confusion between two 

 perfectly distinct tissues — simple striated muscular fibres and 

 compound striated muscular fibres — the former comprising a 

 number of very distinct kinds ditt'ei'ing from one another in the 

 nature of the transverse markings, the latter all conforming to 

 one general type. 



Of the compound striated fibres (with which alone the present 

 paper deals in detail) examples are to be found only in the 

 Clisetopoda (^Syllis, JVephthys), in the Arthropoda, and in the 

 Vertebrata. A detailed account is given of the structure of 

 these fibres in Syllis, where it is sliewn that the number of trans- 

 verse networks in a fibre varies in the case of different species 

 from one to twenty. In the simplest form — as it occurs in the 

 wall of the gizzard of ISyllis nigrojninctata — the compound striated 

 fibre consists of a hollow cylinder, the walls of which are com- 

 posed of fibrils, readily distinguishable in the fresh condition, and 

 bound together in the middle by a single transverse network 

 crossing a median isotropous zone of the fibre with anisotropous 

 zones on either side of it. In a second species (^S. kiriber-giana), 

 there is an increase in the number of transverse networks to three, 

 with a corresponding increase in the number of isotropous and 

 anistropous segments. In iS. schviardia7ia there are' about seven 

 transverse networks, and in S. corruscans there are fifteen to 

 twenty. In the last-named species the fibres are in all essential 

 respects identical with the striated fibres of the Arthropoda and 

 Vertebrata, differing from these only in the greater distinctness 

 of the constituent fibrils and the greater coarseness of the 

 " striations "- — the distance between successive transverse networks 

 being as much as O'OSmm. 



Evidence is adduced in support of the view that each of those 

 compound striated fibres is the equivalent not of a single non- 

 striated fibre, but of a bundle of the latter connected together, 

 first by a single transverse network, afterwards by several ; and 

 in the case of certain species of Polynoe it is shewn that each of 

 the simple fibres which take the place occupied in the same organ 



