EARLY DEVELOPMENT OF HYDRA. I 5 



indistinguishable. The third stage resembles the one just de- 

 scribed, but the hemisphere in which the nucleolar mass lies is 

 also very darkly staining, so much so that the mass within it is 

 often entirely obscured. By sufficiently destaining, however, one 

 can distinguish this mass in almost any pseudo-cell of this sort. 

 The nuclear membrane is broken early in the changes above 

 described and is apparently entirely lost. The last stage is shown 

 in Fig. 21, c, PI. III. The drawings are taken from typical cases 

 and many variations are to be found, but all are easily explained 

 according to the above account. 



Other pseudo-cells of much greater size are frequently found, 

 and their origin can be explained in much the same way. Out- 

 side of the egg one sometimes finds that some of the cells have 

 more than one nucleus, rarely as many as four or five. This 

 fact has already been mentioned, and in connection with it a state- 

 ment as to their probable origin, viz., by the union of two or. 

 more of the primitive ova rather than by the divisions of the 

 nucleus of one of them. This conclusion was the result of the 

 observation that no evidences of divisions in any of the nuclei of 

 these cells were found, though such multi-nucleated cells were 

 not uncommon. If divisions do occur the evidences are for their 

 taking place amitotically, though I am inclined to believe that 

 such divisions do not take place. The metamorphosis of these 

 large cells into pseudo-cells takes place in the same way as that 

 of the single-nucleated cell. 



Occasionally a pseudo-cell of comparatively enormous size is 

 found, such as that shown in Fig. ii, PI. II. These are evi- 

 dently derived from still larger multi-nucleated masses, which are 

 sometimes found outside the egg. Fig. 19, PI. II., shows such a 

 cell with four nuclei and evidences of a fifth. I have found but 

 this one instance, however, and it is therefore very unusual. 

 Brauer ('9i«) has shown a large pseudo-cell in his Fig. 4, PI. X., 

 and they are therefore not an unusual structure. The changes 

 involved in their metamorphosis are probably the same as those 

 already described. No intermediate stages were found and there- 

 fore no figures can be given. 



In no cases have I found convincing evidences of the amitotic 

 nuclear divisions of these bodies such as have been described by 

 Ciamician { ' 79), Doflein ( '97), Allen ( '00) and Tannreuther ( '08). 



