DEVELOPMENT OF ALG^. 75 



becomes rounded. Soon thereafter the cell-contents contract 

 still more, moving towards one end of the cylindrical cell. 

 Then, with a sudden snap, fracture takes place almost en- 

 tirely across the tough coil-wall at a point about one twelfth 

 of its length from one end, that is to say a portion measuring 

 about one twelfth of the length of the whole cell splits across 

 with a perfectly smooth and even fracture, still adhering by 

 a very small portion, and looking like the lid to a box, is 

 thrown back more or less so as to expose the transformed 

 cell-contents to the surrounding fluid. But now the green 

 cell-contents move towards the openings thus formed, and 

 slowly and steadily push themselves outwards, and, being 

 elastic, escape after the manner that a small elastic sac filled 

 with semifluid contents would escape from the hand if pressure 

 were brought steadily to bear upon it. But in tliis case the 

 emergence is not caused by the closing in of the cell-wall, 

 but by a motile power resident in the elastic sac and its 

 contents. It is not shot forth suddenly from the cell-cavity, 

 but squeezes itself out, and as soon as it has escaped assumes 

 the form of a perfect sphere, and, as if exhausted by its 

 previous exertions, comes to a rest. But, although the whole 

 mass is not now in motion, the cell-contents do not remain 

 at rest but go on to another change. The bright sreen. 

 coarsely-granular sphere being at rest, is seen first to become 

 somewhat clearer upon the surface, and evidently a process 

 of difft-rentiation goes on by means of which a very delicate 

 investing membrane is formed, but it is so delicate that it 

 can only with difficulty be seen ; and, -in fact, can hardly be 

 seen to exist as a separate membrane. But upon one side is 

 now seen to appear a bulging outwards of the mass until a 

 nipple-like protuberance is formed which, however, is not 

 filled with the green matter formed elsewhere, but is clear 

 and colourless. Soon thereafter, there is seen to be a slight 

 agitation going on upon the surface of the sphere, near to, 

 and upon one side of the clear space. This movement then 

 assumes a more definite character, and at last a moving cilium 

 is seen to be formed or differentiated from the outermost 

 portion of the globe. Soon another and another are formed 

 in the same manner, attached by their bases around the clear 

 space, and soon, that is to say in fifteen or twenty minutes, 

 a ring of active cilia are seen to surround the nipple-like 

 projection. As soon as they have all made their appear- 

 ance immediately they all begin to move together and in a 

 violent manner, so that motion is imparted to the whole 

 mass, and it swims about actively through the water. Up 

 to this point I find that these changes have been observed 



