58 DEVELOPMENT OF CONNECTIVE-TISSUE FIBERS. 



AMNION. 



A study of the fibrils of the amnion was undertaken in order to see whether 

 the observations of Peterfi (1914) could be corroborated in tissue cultures. Peterfi 

 observed vacuoles within the epithelial cells of the amnion, and concluded from 

 his preparations that these vacuoles fused together and became more numerous 

 in the cells of the amnion of chick embryos of from 3 to 5 days' incubation. Accord- 

 ing to Peterfi, the walls of these vacuoles contain a substance which is different 

 from the remainder of the cytoplasm, and as the walls fuse together they form a 

 network of elastic fibers over the epithelial cells of the amuion of a chick embryo 

 of 7 days' incubation. My observations on the amnion in tissue cultures did not 

 show this. The epithelial cells contained varying numbers of vacuoles, most of 

 which stained with neutral red, though a few remained unstained. Fibrils are 

 formed, but, so far as can be determined from these observations, they are formed 

 from the exoplasm of the cell, regardless of the vacuole, in practically the same 

 manner as are the fibrils of the connective-tissue cells (plate 2, fig. 9). 



CONCLUSIONS. 



1. The connective -tissue fibrils begin to develop in the subcutaneous tissue 

 of chick embryos of from 9 to 10 days' incubation, and appear as well-developed 

 fibers in the subcutaneous tissue of a 12-day chick embryo. The new growth 

 from explanted pieces of subcutaneous tissue from chick embryos of 8 to 10 days' 

 incubation proved the most satisfactory for the study of the connective -tissue fibers. 



2. The cut fibers which are present in the explanted piece of 11-day to 15-day 

 chick embryo subcutaneous tissue do not grow either in length or bulk in the tissue 

 cultures. 



3. The new growth of connective tissue is exceedingly sensitive and reacts 

 by a contraction of the cell from the outer edge in towards the explanted piece. 

 This contraction does not cause the formation of fibers in the new growth. 



4. Fibers are not present in the 24-hour growth from even 12-day to 15-day 

 chick-embryo tissue, but develop in the cells of the new growth from delicate 

 fibrils in the exoplasm of the cells after 24 hours. 



5. The fibrils developed as delicate lines of the exoplasm of the cell; they 

 became gathered into bundles which passed from cell to cell, and the bundles 

 later passed over or through the exoplasm of several cells as a definite fiber. The 

 fibers never became so adult that the individual fibrils which make up the fiber 

 could not be traced into the cytoplasm of some cell, whether near or distant from 

 the main body of the fiber. 



6. Although the new growth, when closely attached to the smooth cover - 

 slip, often takes the form of a membrane, and although this membrane exhibits 

 the cell pattern which is characteristic for endothelium when treated with silver 

 nitrate, nevertheless there is no evidence that these cells have become endothelial 

 cells; they still retain the characteristics of connective-tissue cells, and many 

 form fibrils. 



