152 



Fig. 11. The same, uncontracted (x3000). Note the "spHtting" of the striations 

 (Hensen's line). 



Fig. 12. Developing leg muscle of a chalcid wasp (Nasonia). One myoblast is seen 

 in mitosis (x about 1500). 



Fig. 13. A small part of one of the columns of myoblasts which results secondarily 

 from a splitting of the mass seen in fig. 12. 



Fig. 14. The same undergoing fibrillation. Striations not yet visible (x2000). 



Plate XIII. 



Fig. 15. Fibrillae from leg muscle of a myriapod (Scufigcra) in various stages of con- 

 traction. The reversal of the striations is obvious (x3400). 



Fig. 16. Transverse section of one of the pair of bands of thoracic myoblasts, which 

 will produce the five wing-moving muscles of the imago. Taken from a metamorphosing 

 larva of Nasonia (x about 1100). 



Fig. 17. The same, several hours later. Five syncytial columns have been formed. 



Fig. 18. The same, at a slightly later state of development. Note the increase in size 

 of the five columns. Some myoblasts are seen in mitosis (xl200). 



Fig. 19. Longitudinal section of one of the syncytial columns at a later stage of develop- 

 ment (xl200). The section cuts along the line of junction of the syncytial column and the 

 surrounding myoblasts, and the latter are seen giving oil long processes (sarcostyles) into the 

 syncytial mass (sarcoplasm). Many myoblasts have been omitted from the drawing so as 

 to give greater clearness. 



Plate XIV. 



Fig. 20. A motor nerve-ending, from muscle of frog. Notice the relation of the 

 end-plate nuclei to the Krause's membranes. Striations have not been drawn (x about 2000). 



Fig. 21. Longitudinal section along middle of leg muscle fibre of Scutigcra, to show 

 relation of nuclei to Krause's membrane. The fibre is contracted, so that Krause's membrane 

 is hidden by the dark material (striation). 



