68 CHIMvEROID FISHES AND THEIR DEVELOPMENT. 



blastomere the nucleus has undergone, or is undergoing, amitosis. Now in these 

 instances there can be no question that the amitotic divisions are taking place within 

 the blastoderm itself, in a region where, by analogy, mitosis alone should occur, 

 and where later, indeed, in the same form, mitoses alone are found. And we are 

 thus constrained to conclude either that amitosis and mitosis are processes not as 

 immutably different in fate as is generally assumed, or that at a later period the 

 amitotic blastomeres undergo disintegration within the blastoderm. 



But to continue: In fig. 64 c, from a neighboring section, we observe as before 

 amitosis occurring within the germinal wall, and this type of nuclear multiplication 

 appears active to an extraordinary degree, as the detail, i, indicates. Moreover, 

 with this activity, there is evidence from the greatly elongated character of some 

 of the nuclei, 2, 2, and from the evident trails which occur, e. g., at 3, that these 

 nuclei are passing rapidly in the direction of the surface of the yolk. We note also 

 that cellular increments, e. g., in such a cell as 4, are arising from the germinal 

 wall, and, as in the former specimen, amitotic division is present, 5, in the blasto- 

 derm proper. Adjacent to this, and in as close relation with the germinal wall, 

 there is also evidence of mitotic division, 6. We have seen that in this section the 

 cell 4 is arising out of the germinal wall ; if any doubt exists as to possibility of 

 cells to arise from the germinal wall at this late stage, we may refer to the detail 

 shown from a neighboring section in fig. 64 D. Here is present a row of cells 

 arising in this manner: in the wall itself occur the nuclei 2 and 3, of which the 

 latter is passing into a lobe-shaped process budding outward from the germinal 

 wall. From their position we may safely conclude that 4 and 5 have arisen in a 

 similar way. We observe, finally, that the nucleus in cell 5 is undergoing changes 

 in the direction of amitotic division. 



Another interesting detail is given in fig. 64 E. We have here two cells which 

 appear to have arisen side by side from the germinal wall; the cytoplasm of one is 

 clearer, more differentiated apparently than its neighbor, which contains fine yolk, 

 yet the nucleus of the cell lacking in yolk is undergoing amitotic division, while 

 that of its neighbor is dividing mitotically. In other sections in this series we note 

 the following details: Fig. 64 F, a cell half budded from the germinal wall, also a 

 pair of cells evidently in stage of telophase, of which the lower appears to have just 

 budded out from the germinal wall; fig. 640, two reticular nuclei in the germinal 

 wall, products of amitotic division (cf. fig. 640), in one of which are two large 

 chromatin masses; fig. 64 H, nucleus undergoing a complicated series of amitotic 

 divisions; this occurs near the surface of the germinal wall, and we note the 

 presence of vacuoles, three in number, lying immediately above the main masses 

 of the dividing nuclei ; fig. 64 i, within the outline of a single large blastomere occur- 

 ring in the blastoderm proper, three cells appear, and two of these appear to 

 have been derived from the largest, in which we observe as many as half a dozen 

 nuclei; fig. 64;, a cell in a late stage of division which shows three nuclei already 



