Spiral Structure of Muscle. 91 



pying a middle place ; but here it must be remarked, that striking 

 differences would certainly have been met with had Bowman's 

 researches been of a more special kind ; for it is probable that 

 the salamanders and other naked Amphibia would have presented 

 still larger fasciculi than even Fishes. 



Schwann was the first to make us acquainted with the exist- 

 ence of the sarcolemma. An independent discovery of it was 

 made by Bowman, to whom it is that we are indebted for an 

 exact description of that structure and an appropriate name. Its 

 mode of formation out of spirally arranged cells, the author 

 believes to have been first seen and published by himself. That 

 mode of formation of the sarcolemma appears to be as follows : — 

 At a, fig. 13, is a coil of young cells (once a column of com- 

 pound cytoblast, as at fig. 20 c). a, in fig. 13, is a drawing 

 from nature; b in the same figure is a diagram, a passes into b. 

 That the spirals really do consist of cells is seen from fig. 14, a 

 drawing from nature, in which a represents a large double spiral 

 from the tail of the tadpole when very young, and b the remains 

 of a similar double spiral after the addition of acetic acid. The 

 acid removed the coalesced membranes of the cells, of which the 

 double spiral a was composed, and left the nuclei behind in 

 double spiral ordei*. At c is seen the structure of one of those 

 nuclei. They contained the elements of division, by which divi- 

 sion the spirals pass into the state of membrane. And fig. 15, 

 also from nature, shows such tUvision to have taken place ; this 

 figure representing a stage in the formation of the sarcolemma. 



With regard to the function performed by the sarcolemma, no 

 definite opinion appears to have been given. The author believes 

 that its function depends on elasticity. As the walls of the sar^ 

 colemma-cylinder are distended during the contraction of the 

 double spiral threads, they return inwards as soon as relaxation 

 comes on. And it is in this manner that the active relaxation 

 of the fasciculus of muscle is to be explained. 



Muscle from the thigh of the Grasshopper (of which many 

 individuals, including several species, were examined) having 

 uniformly presented a relaxed state nearly a])proaching to that 

 in fig. If) (which, however, is merely a diagram), it appeared to 

 the author probable that such a state was not unconnected with 

 the sudden muscular contractions required by this creature for 

 its leaps. A sudden change from such a state of relaxation to 

 that of extreme contraction must here take place with the great- 

 est facility, and be combined with the manifestation of great 

 power. This opinion having been mentioned to Prof. Purkinje, 

 the latter recommended the author to examine the corresponding 



