140 JEREMIAH S. FERGUSON 



ing cognizance of the plasticity of the connective tissue cellular 

 cytoplasm, and also of the active motion of connective tissue cells 

 during the period in which the fibers are being formed, so that the 

 finer connective tissue fibers become, by the cellular activity, 

 embedded in the plastic cytoplasm of the cells during their stereo- 

 tropic locomotion. The plastic character of the cellular cyto- 

 plasm is admirably shown by the rapid changes in form of the 

 connective tissue cells in the fins of living fish embryos. 



I have already stated that the spindle cells of connective tissue 

 in the fins of living fish undergo active locomotion. In fact this 

 seems to be a most prominent function of the spindle cell type. 

 Most frequently the cell glides along connective tissue fibers which 

 often appear to be thus partially enveloped by the cytoplasm. 

 In recording this stereotropism I am able to corroborate, for the 

 living cells of embryo fish, the observations of Harrison on tissue 

 cultures in which he finds that the connective tissue cells are spe- 

 cially prone to follow along the surface of fixed objects. Such ob- 

 jects in normal living subjects are most frequently the connective 

 tissue fibers and fiber-bundles already deposited, though as pre- 

 viously stated, I have also observed connective tissue cells moving 

 along the surface of the dermal fin rays and of blood-vessels. 

 In this form of activity the cells adapt themselves more or less to 

 the shape of the surface along which they are moving. They 

 wrap themselves about or rotate around the finer fibers (fig. 3) 

 and they flatten themselves against the larger objects (figs. 2, 

 3 and 5). In this attenuated condition they still move along the 

 surface of fibers, often at a considerable rate of speed. One such 

 cell I have recorded in a preliminary communication 4 was found in 

 ten minutes to have covered a distance of 50/*, a rate of In in 

 every twelve seconds. 



The striking similarity of the living, spindle, connective tissue 

 cells to those of fixed tissue is indicated in fig. 10 which shows 

 several such cells from a 100 mm. pig embryo. The magnifica- 

 tion is the same as that used for the observation of the living cells. 

 Thcsimilarity in the form of the cell and the relation of cells to 

 fibers is apparent on comparison with the preceding figures. One 



* Biol. Bull., vol. 21, page 272, fig. 2, 1911. 



