REACTION OF EMBRYONIC CELLS TO SOLIDS 527 



almost immediately. None of the unsupported ones gave positive 

 results. 



Series III. This series of twenty-four experiments was de- 

 signed to test rigorously the influence of the spider web upon the 

 movements of the tissue, and as the preliminary experiments 

 indicated that serum afforded a better medium than the inorganic 

 solutions, the former alone was used. The serum was obtained 

 from three different specimens of Rana clamitans, a species 

 different from that of the embryonic tissue isolated. The cul- 

 tures in this series were made in pairs. The central nervous 

 system with some mesoderm attached was dissected entire out 

 of the embryo in saline solution. It was then divided into two 

 parts, one part being mounted upon web and the other in a plain 

 hanging drop. In some cases the cephalic half of the medullary 

 cord was placed on the web and the caudal half in the plain drop, 

 while in others the order was reversed. The results of this series 

 were entirely convincing. Out of the twelve preparations 

 mounted upon the web eleven showed characteristic wandering 

 of the cells with definite relations to the web fibers (fig. 1). The 

 remaining one was disarranged accidentally the first day and 

 gave no results. Cell movement began in some cases as early 

 as eight hours after explantation and on the day following it was 

 in full swing in all of the cultures. Of the twelve mounted in the 

 large drops none showed any movement of cells except one of 

 the cases in which the drop spread out, allowing the tissue to 

 come into contact with the cover (fig. 3).^^ In this one case 

 six days after the culture was made a number of cells appeared 

 on the cover and later some pigment cells were found. In the 

 large drop preparations the isolated cells, which soon became 

 very numerous,^^ always remained rounded (fig. 2), but in spite 

 of considerable disintegration into single cells the main mass of 

 tissue was in every case left intact. That it was alive was 



1^ The figure, which is much like the preparation referred to, was drawn from 

 another case. 



^^ In this respect embryonic frog tissues differ markedly from those of the chick, 

 in which the elements remain closely bound together and the whole mass rounds 

 off its outer surface (see p. 539 and figs. 11 and 14). 



