212 PROTOPLASM 



shown beyond a doubt that they are in mutual contact. 

 This is especially shown by the fact that the larger drops 

 which are apposed to one another are distinctly flattened at 

 the surface of contact. Bound each drop the above-men- 

 tioned clear diffraction ring is to be seen, which is distinctly 

 marked off by a darker border from the rest of the less 

 brilliantly illuminated field of vision. If the tube be 

 lowered just a little, the droplets diminish in size and become 

 dark, as is the rule with strongly refractile drops ; at the 

 same time the image of the larger ones becomes dis- 

 tinctly polygonal, which confirms what has been remarked 

 above concerning their direct contact and mutual flattening 

 (see Plate X. Fig. 5, a, I). The images of the droplets 

 now no longer touch one another, but are separated by 

 light intervening spaces. These intervening spaces are dis- 

 tinctly crossed by faint, moderately dark filaments, which 

 unite the dark images of the droplets to one another. In 

 this way quite an exquisite network comes to be formed, 

 with nodal points of considerable thickness. The meshes of 

 this network are always triangular, the trabeculae for the 

 most part very fine, but occasionally also much thicker. 



The origin of this network is easily explained if one 

 studies attentively the most external drops of such groups. 

 It is then seen that the diffraction ring with its dark border, 

 described above, is present round each of the droplets ; but 

 since the dark borders of neighbouring diffraction rings run 

 into one another, and at the same time pass across adjacent 

 droplets, the connecting filaments are shown to be portions 

 of the dark borders of the diffraction ringjs. As lono- as a 



o o 



border of this kind coincides with an adjacent droplet it is no 

 more visible. The thicker connecting filaments also admit 

 of a simple explanation. In the smallest droplets, as a rule, 

 the dark borders of two neighbouring diffraction rings fall 

 so close together that they give the appearance of a common 

 connecting filament between the two drops. If, on the other 

 hand, two such borders are farther apart, a dark connecting 

 bridge of greater thickness comes into view, since the whole 

 intervening space between these adjacent borders appears 

 darker. As a rule, each one of the triangular meshes of the 



