OBSERVATIONS ON STRIPED AND UNSTRIPED MUSCLE. 105 



tudinal fibrils have ceased to contract ; they are possibly also 

 paths for the nervous impulse. 



4. In some cases where muscle has been hitherto described 

 as striped, but gives no appearance of the network or treatment 

 with the gold and other methods, the apparent striation is due 

 to optical effects caused by a corrugated outline in the fibre. 



5. In muscles which do not perform rapid movements, but 

 whose contraction is comparatively slow and peristaltic in 

 nature, this peculiar network is not developed. In most if not 

 all of the invertebrate unstriped muscle there does not appear 

 to be an intracellular network present in any form, but in the 

 vertebrate unstriped muscle a network is present in the form 

 of longitudinal fibrils only ; this possibly represents a form of 

 network intermediate between the typical irregular intra- 

 cellular network of other cells and the highly modified network 

 of striped muscle. 



6. The cardiac muscle-cells contain a network similar to that 

 of ordinary striped muscle. 



The investigations connected with this paper were partly 

 carried on in the laboratories of the Owens College and 

 partly at the Scottish Marine Station at Granton. I must 

 here express my thanks to my brother, Professor Milnes 

 Marshall, for his kindness in revising the paper, for much 

 advice in its production, and for obtaining the literature of 

 the subject; all the controversial points were discussed with 

 him and the preparations submitted to his examination. My 

 thanks are also due to Dr. Klein for kindly showing me his 

 preparations and for examining several of my own. I must 

 also thank Mr. J. T. Cunningham for the use of the Scottish 

 Marine Station, and for obtaining several of the animals. 



