No. I .] SPERM A TOGENESIS OF BA TRA CHOSEPS. I 5 



Cytoplasmic Membrane and Cell Wall. — The cell wall is un- 

 doubtedly the most constant structure of the cell. I have not 

 made this structure the subject of any particular study and can 

 only say that it appears to be composed of minute granules, 

 closely approached to each other and evidently of the same 

 nature as the granula composing the cytoplasm of the cyto- 

 some. The formation of the new cell wall between the two 

 new daughter-cells will be described under the general heading 

 of mitosis. Here I will only mention that the new wall is 

 formed by the aid of metaplasmic secretions from the outer 

 sphere. All through the evolution of the cell we find that 

 wherever large vacuoles are formed in the cell, these seem to 

 become surrounded by a thicker cytoplasm or incipient membrane. 

 This is, I think, especially the case when these vacuoles contain 

 some substance differing in quality from that surrounding them, 

 in which instances the cytoplasm appears to thicken into a 

 veritable membrane, greatly resembling a thin cell wall. 



At a certain stage in the mitosis of the cell, when in the end 

 of the anaphase the new nucleus is beginning to increase in 

 size, a new membrane is formed surrounding the nucleus, but 

 at a considerable distance from it. This membrane is not a 

 nuclear membrane, but a true cytoplasmic membrane, which is 

 again dissolved, as soon as the new nucleus has reached its 

 final or desired size. This membrane only serves as an attach- 

 ment for the cone fibers, and by being pulled outwards causes 

 a large vacuole to be formed around the nucleus, thus giving 

 the nucleus ample room to expand and to grow (Figs. 59-68, 

 also Fig. 70). The nuclear membrane is formed later, imme- 

 diately around the chromosomes, often while the cytoplasmic 

 membrane is still in existence, as, for instance, in Fig. 70. 

 Later on this cytoplasmic membrane is dissolved. The process 

 of the formation of this false nuclear membrane, as well as of 

 \he inner and thinner membranes around the vacuoles, and of 

 the cell wall itself, is, I think, one and the same, a condensing 

 of the cytoplasmic granules. In the formation of the new cell 

 wall the draught on the cytoplasm is so great that an extra 

 supply of cytoplasm and nutriment is required, which supply is 

 furnished by the plasmosphere and its metaplasmic secretions. 



