492 Wisconsin Academy of Sciences, Arts, and Letters. 



matophores of similar structure were being observed in the two 

 cases provided only surface vie^vs were studied. Artari does 

 not attempt to solve the problem as to the mechanism by 

 which the so-called chromatophore is divided. His account of 

 the cleavage process is no doubt influenced by the conception 

 of the Vollzellbildung of Strasburger in connection with nu- 

 merous other forms as noted above. That he observed only the 

 later stages in the process is evident from the work of Ivlebs 

 and the figures that I have shown in this connection. 



Klebs (16) gave a very complete account of the appearance 

 of the Hydrodictyon cell under various conditions and de- 

 scribed the process of cleavage as taking place in a manner en- 

 tirely different from that described by previous observers. 

 KlebSj however, like his predecessors, limited his observations 

 to surface views of the material for the most part in the living 

 condition. He confirms Braun's statement that there are three 

 distinct layers of protoplasm in the cell, but identifies the outer 

 as the hautschicht and the inner as the vacuolar membrane or 

 tonoplast of De Yries, leaving the middle layer occupied by 

 the chromatophore and the layer of protoplasm containing the 

 nuclei. Klebs' account of tlie structure of the chromatophore 

 is essentiallv the same as that of Artari. He thinks that while 

 this is a distinct chromatophore it is of a Ioav order of organi- 

 zation since it is merely passive during the process of cleavage 

 and shows at no time the initiative power of reproduction. 

 The nuclei are said by Klebs to occupy no definite position 

 with reference to the pyrenoids, but to appear in the openings 

 through the chromatophore as if lying deeper in the protoplasm. 

 They are described as vesicular structures each having a single 

 large central nucleole. The nuclei, like the pyrenoids, are 

 connected by special strands of protoplasm foimiing a network 

 with tJie nuclei at the anodes of the meshes. 



The process of cleavage begins, according to Klebs, by the 

 formation of angular, in some cases almost canal like, vacuoles 

 in the middle layer of protoplasm. The vacuoles fuse \\dth one 

 another so as to cut the protoplasm, including the chromato- 

 phore, into large irregular pieces which, by constriction or by 

 further branching of the vacuoles, are cut into smaller pieces 



