288 Papers from the Department of Marine Biology. 



8. The evidence is unequivocal against an interpretation of structure 

 in terms of "muscle-cells" and intercellular myofibrillse. 



9. The nuclei of the growing muscles multiply by amitotic division. 



10. The myofibrillse may be resolved into still finer fibrils to the 

 limit of visibiUty, an observation in support of Heidenhain's "teil- 

 korper" ("protomere") theory. 



11. The structurally different constituents of the Limulus sarcostyle 

 are the Z-membrane and the Q and J disks. Q and J most probably 

 differ only in the matter of a relatively greater abundance of certain 

 darker-staining materials, the so-called anisotropic granules, in the 

 former. 



12. M-membranes occur only in certain more specialized types of 

 striped muscle ; they are probably never present in the form of actual 

 membranes in cardiac muscle. 



13. In essential structure the cardiac and skeletal muscles of Limulus 

 are closely similar, indicating a close functional similarity. The struc- 

 ture serves, moreover, as a splendid illustration of the "law of bio- 

 genesis," in that it is practically identical with a stage in the early his- 

 togenesis of striped muscle of teleosts. 



