THE BIOLOGY OF THE CELL SURFACE 



sea-water made more concentrated by evaporation. In 

 calcium-free sea-water, the ectoplasm of sea-urchins' eggs 

 fairly bristles with delicate filaments. In other eggs also 

 the presence of these filaments can be demonstrated by 

 experimental treatment — especially by placing the eggs In 

 hypertonic sea-water. It Is to be emphasized that the 

 experimental means does not cause the formation of these 

 filaments but only makes them more easily visible. Thus, 

 In eggs of Nereis and of Platynereis the ectoplasmic fila- 

 ments, seen In the unfertilized eggs as ectoplasmic strlatlons 

 and for a short time after fertilization as strands, can always 

 be more strongly revealed In later stages, when they are 

 seen with greater difficulty, by submersing the eggs In 



sea-water made hypertonic by the 

 addition of NaCl or KCl. The same 

 observation has been made on eggs of 

 other worms, for example, on those of 

 Sabellaria (Fig. 17). The often ex- 

 pressed opinion that the ectoplasmic 

 prolongations thus made visible are 



Fig. 17. — Egg of Sabel- r , • i i i r 



laria alveolata to show artefacts leaves Unconsidered the fact 

 effect of hypertonic sea- that the cggs show normally an ecto- 

 water on the ectoplasm pi^smlc Structure, as has been abun- 



(after Faure-Fremiet). 



dantly proved for eggs from those of 

 sponges to those of vertebrates. The descriptions In the 

 literature admit of no doubt on this point. 



When we place alongside this fact the observations 

 detailed by students of tissues In culture on the strongly 

 expressed ectoplasm, the generally accepted fact of ecto- 

 plasmic structures In Protozoa together with the evidence 

 of Intercellular connections between cells In tissues and the 

 knowledge of the mode of union of nerve-cells by processes, 

 we have very good reason for asserting that the filaments 

 and prolongations of the ectoplasm are Its characteristic, 

 and perhaps its most Important, structure. They have 



102 



