DESCRIPTION OF PLATES. 



PLATE I. 



Fid. 7. Photograph of a fixed preparation of the growth from the heart of a 6-day chick embryo. Culture 48 hours 



old. Oc. 4, lens 16 mm. 

 Fia. 8. Photograph of a fixed preparation of the growth from the skeletal muscles of a 9-day chick embryo. Culture 



48 hours old. Oc. 4, lens, 16 mm. 

 Fio. 9. Photograph of a fixed preparation of the growth from the amnion of a 5-day chick embryo. Culture 48 



hours old. Oc. 4, lens 16 mm. 

 Fia. 10. Photograph of the protoplasmic end of a muscle sprout. The contractile substance is coagulated in the 



form of bun lie? of threads. Culture 48 hours old, from skeletal muscle of 8-day chick embryo. 

 Fia. 11. Cross-striated muscle fibers in growth from skeletal muscle of a 10-day chick embryo. Culture 5 days old. 



Fixed by means of Zenker's solution without acid. Stain iron-hemato.xylin. Oc. 6, lens 2 mm. 



PLATE II. 



Fia. 12. An epithelial cell lyin^ side by side with the smooth-muscle cell of fig. 17. It is not elongated, does not 



contain coagulated contractile substance, and the mitochondria are not long threads. 

 FIG. 13. Three cells observed while undergoing rythmical contraction and later fixed by means of Zenker's solution. 



C, the contraction node. Culture 25 hours old, from amnion of 8-day chick embryo. Oc. 4, oil-imm. 

 FIG. 14. Smooth muscle from the amnion of an 8-day chick embryo. Culture 48 hours old. Fixed with 10 per cent 



nitric acid. Stained with Mallory's connective-tissue stain. Curled edges of cell stain as elastic fibers, 



while the coagulated remains of intercellular bridges appear as a connective-tissue network. Oc. 4, oil-imm. 

 FIG. 15. The star-shaped arrangement of the muscle fibers of the amnion of 5-day chick embryo. Oc. 6, lens 16 mm. 

 FIG. 16. A group of smooth muscle-cells from the amnion of a 4-day chick embryo. Culture 48 hours old. The 



contractile substance is coagulated into bundles of gray threads. Osmic vapor, iron hematoxylin 



and eosin. Oc. 6, lens 3 mm. 

 Fio. 17. Spread-out smooth-muscle cell from the edge of the growth. The coagulated contractile material can be 



distinguished from the elongated mitochondria. Culture 48 hours old from 5-day chick embryo. 



Oc. 4, oil-immersion lens. 



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