94 Geometrical relation of Nuclei 



Many also are broken; but floating among the debris are 

 hundreds of isolated cells as well as pairs and aggregates of three 

 and more. Many of the cells are quite spherical as soon as one 

 gets the preparation under observation. Other cells are oblong, 

 or compressed in some way or other, and are seen to assume 

 slowly a more and more spherical condition. Some of the pairs 

 are so placed that the individuals touch one another at a point 

 only, others are flattened against one another. The latter are 

 probably cells in the act of division. 



I have seen isolated cells which are quite close to one another 

 come in contact, but I have not seen them flatten up against each 

 other. 



Isolated cells which are farther apart sometimes show less rapid 

 and less regular attraction movements. For instance : there were 

 two cells separated from each other by 6-5 divisions of the micro- 

 meter. The one on the left, the larger of the two, moved only 

 slightly; the one on the right, the smaller, moved considerably, 

 so that eventually they were only 2-0 divisions apart. The move- 

 ments were of two kinds, slow sliding movement and sharp jerks. 



But many of such movements, obviously, need have nothing to 

 do with attraction and are amoeboid. 



There are undoubted changes of shape in the isolated cells. 

 The first tendency on separation is towards the assumption of a 

 spherical form. This is followed by more or less marked changes 

 in shape, sometimes so great as to amount to the protrusion of 

 pseudopodia. So that it is probable that the slower and less certain 

 movements are due to amoeboid activity, and the approximation of 

 two cells may be fortuitous. And if the protrusion of pseudopodia 

 is evidence of the contractility of some part of the cytoplasm of the 

 cell, then clearly the cells must at this time be capable of contractile 

 movements, which if applied in a particular way would bring 

 about the invagination of the blastula as Professor Bateson 

 suggests. 



Thus in Fig. 41, two isolated blastomeres from a toad's egg in 

 the gastrulating stage are shown as they appeared at intervals 

 between 5.30 p.m. and 7.30 p.m. on April 15. In this case the 

 slight reduction in the distance between the two cells must almost 

 certainly have been due to the amoeboid movements exhibited 



