OBSERVATIONS ON STRIPED AND UNSTK1PED MUSCLE. 91 



Frog (fig. 10) and Bird (fig. 11); the network in the latter 

 animal is much plainer than in the others. 



The striation of cardiac muscle therefore appears 

 due to an intracellular network similar to that of 

 ordinary striped muscle. 



Unstriped Muscle of Vertebrates. 



Klein 1 describes in the unstriped muscle of vertebrates a 

 bundle of longitudinal fibrils which are in connection with the 

 intranuclear network. This description of the structure of 

 the unstriped muscle-cell is as follows : " Thus we may regard 

 the unstriped muscle-fibre as composed of a sheath with annular 

 thickenings and a bundle of delicate fibrils which at one more 

 or less central point forms a delicate network. This, sur- 

 rounded by a special membrane — except where the network is 

 in connection with the bundle of fibrils — represents the nucleus/' 

 Klein regards the bundle of fibrils as the contractile part of 

 the cell, and thinks that by their shortening the muscle-fibre is 

 caused to contract, elongation being produced by the elastic 

 rebound of the sheath. Flemming 2 has observed these fibrils 

 in the living muscle. 



Dr. Klein informs me that he regards the bundle of 

 longitudinal fibrils as representing an intracellular network 

 homologous with other intracellular networks. Dr. Klein 

 has been kind enough to show me his preparations of unstriped 

 muscle prepared from the mesentery of the newt by twenty-four 

 hours immersion in 5 per cent, ammonium bichromate, and 

 afterwards stained with logwood. These preparations show 

 clearly the longitudinal fibrils and their connection with the 

 intranuclear network. 



I have made preparations, by the gold method, of muscle 

 from the mesentery of the newt and from the bladder of the 



1 Klein, ' Atlas of Histology,' p. 74, pi. xv ; also ' Quart. Journ. Micr. 

 Sci.,' 1878. 



2 " Beobachtungen iiber die Bescliaffenheit des Zel). Kerns," ' Arch, fur 

 Mikr. Anat.,' 1876, Bd. xiii, pp. 714, 715. 



