5o8 T. GUSTAFSON 



Discussion 



Allen : This is a remarkable demonstration of the importance of cell movement 

 in embryonic development. I was particularly interested to observe that there are 

 two kinds of amoeboid movement represented which were ordinarily separated by 

 those of us who are interested in cellular motility. I see formation of both lobopodia 

 and filopodia ; the principal difference between these two kinds of pseudopodia is 

 that the pattern of streaming in the lobopodium is that of a fountain, whereas that 

 in a filopodium is two directional streaming. So far we do not know whether these 

 two kinds of movement have similar mechanisms. I wonder if you have looked 

 carefully at the filopodia to find if there is in fact streaming in two directions ? 



Gustafson: No, I haven't, but during my last sojourn at Kristineberg's 

 Zoological Station we filmed larvae for days at one-second intervals just to investi- 

 gate the dynamics of the pseudopods. 



Holter: I was very much interested in your evidence for areas of stickiness 

 that seem to play a determining role in morphogenesis. Isn't there any possibility 

 to determine chemically by means of surface reactions, what would be the reason 

 for this surface stickiness ? 



Gutsafson: I have not tried, but I am very interested to do so. 



RuNNSTROM : I can tell you that in our experiments very low trypsin concen- 

 trations (treatment with lo ~^-io^ ",, trypsin for 15 min.) induce stickiness of the 

 sea urchin egg. This may indicate a possible role for proteolytic enzymes. 



Gustafson : In this connection I may mention that if one treats the eggs with 

 very weak detergent solution one completely changes the pattern of development 

 of the ectoderm : the mesenchyme ring and the main ciliated band form at wrong 

 places and so on. This may give some indication of what lies behind the stickiness 

 in the cells. 



Porter : Your observations suggest that there might be some guiding frame- 

 work in the blastocoele for the mesenchymal cells ; is there fibrous material there ? 



Gustafson : One can often see a lot of particles in the blastocoele which swim 

 around with great speed. This suggests that there are no rigid structures in the 

 blastocoele at this stage of development. Occasionally, however, one can see 

 particles lined up and vibrating together in a way which suggests the presence of 

 some submicroscopic or at least thin and transparent fibres. 



Runnstrom : As shown by my colleague J. Immers, there are sulphated 

 polysaccharides present in the blastocoele of the sea urchin embryo. In a late 

 blastula stage these polysaccharides become linked to proteins. The migrating 

 cells which Ciustafson has studied are in fact surrounded by a coat of a protein-acid 

 polysaccharide complex, a fact that probably is of importance for understanding the 

 behaviour of the migrating cell. If the coat is imperfectly formed the migration of 

 the cells is disturbed or prevented (the latter occurs following pronounced 

 animalization of the larvae). 



