100 C. F. MAESHALL. 



should expect to be differentiated first. In the embryonic 

 development of striped muscle it is found that the longitudinal 

 striation appears first, i. e. that the longitudinal bars of the 

 network are differentiated before the transverse. This is also 

 the case in regenerating muscle. Again, in tracing the phy- 

 logeny of muscle, we found that the first indication of an 

 intracellular network was in the vertebrate unstriped muscle 

 in the form of longitudinal bars only. Hence both the phy- 

 logeny and the ontogeny of the network favours the view 

 that the longitudinal bars are the contractile part of the 

 cell. 



Action of the Transverse Networks. 



Similarly to the longitudinal bars the transverse networks 

 always remain straight in all conditions of contrac- 

 tion relaxation of the fibre. Hence they become necessa- 

 rily extended when the muscle-fibre contracts, and return to 

 their original form on relaxation of the fibre. The question 

 now remains as to whether the return of the transverse net- 

 works to their original position is due to active contrac- 

 tility or to elastic rebound. The following arguments, for 

 the first of which I am indebted to Mr. Melland, are in 

 favour of the latter view. 



(a) An elastic thread, if stretched and then allowed to 

 rebound, will always return to its original length, i. e. will 

 always shorten to the same extent. The transverse networks 

 behave in this way ; they always shorten to the same extent, 

 viz. to the normal diameter of the fibre. This speaks in favour 

 of their being passively elastic, for if they were actively con- 

 tractile there is no reason why the fibre should not be com- 

 pressed to less than its normal diameter, elongation at the 

 same time taking place ; whereas the fibre always relaxes to 

 the same extent. 



(6) If the statements of Gerlach, Retzius, and Bremer are 

 correct, both parts of the network are connected with the end- 

 plate and with the axis cylinder of the nerve, the longitudinal 

 bars being connected indirectly through the transverse net- 



