204 The Fibrils of the Heart Muscle Cell of the Chick 
MIGss Tome: 
The accompanying figures are camera lucida drawings made at table level. 
In all cases the magnification is about 2000 diameters. 
Fie. 1. Longitudinal section of heart muscle cell from a 30-hour embryo. 
The cytoplasm shows an irregular network. 
Fig. 2. Cross section at 30-hour stage. 
Fig. 8. Longitudinal section, 72-hour stage. 
Fig. 4. Cross section, 72-hour stage. 
Fic. 5. Longitudinal section, 96-hour stage. 
Fics 6 and 7. Cross sections, 96-hour stage; Fig. 6, above or below the 
nucleus; Fig. 7, through the region of the nucleus. 
Fig. 8. Longitudinal section, 120-130-hour stage. 
