hargitt: pennaria tiarella and tubularia crocea. 171 



the spindle is therefore in an advanced stage. The number of chro- 

 mosomes in this egg cannot be stated with confidence, though the six 

 spherical bodies are certainly egg chromosomes, and several smaller, 

 deeply staining bodies near by may be of similar import. The number 

 of chromosomes left in the egg after the formation of the second polar 

 cell cannot be more than ten, and may possibly be less. 



While these maturation figures leave much to be desired in clearness 

 and ease of interpretation, they do show without doubt that the polar 

 cells are formed by a more or less regular mitosis. 



A somewhat unusual condition is shown in Figure 14. Two other 

 eggs in the same medusa have large ellipsoidal germinative vesicles 

 without nucleoli and with a dense cytoplasmic layer about the germina- 

 tive vesicle, such as is shown in Figures 5-7, which represent the 

 condition occurring just before the formation of the first polar cell. 

 A fourth egg in the same medusa has the nucleus in the condition 

 shown in Figure 18. The eggs in this medusa were consequently at a 

 stage corresponding very nearly with that of the formation of the polar 

 cells. The nucleus shown in Figure 14 is apparently in the so-called 

 resting condition, the chromatin being in the form of a diffuse and 

 feebly staining network. Strongly marked cytoplasmic radiations are 

 directed to a point at the surface of the egg which is slightly peripheral 

 to the outer end of the nucleus ; but no centrosome could be found at 

 this point, and no other radiations were present in the egg. Outside 

 the egg, and also outside the jelly-like membrane which surrounds it 

 while it is within the medusa, is a body which closely resembles the 

 first polar cell shown in Figure 13. There is at one end a deeply 

 staining granular mass, apparently chromatin, and stretching from 

 this mass toward the opposite end of the body there is an arrangement 

 of the granules which gives the body a faintly striate appearance. 

 The fact that this body is outside the membrane rather than inside it, 

 as in the polar cells shown in Figures 12 and 13, may be an argument 

 against considering it a polar cell; but it seems not unreasonable to 

 suppose that the body may have been forced through the jelly-like 

 envelope, which in the living animal is probably soft. Considering 

 all the evidence, it is hard to escape the conclusion that we have here a 

 stage between the formation of the first and the second polar cells. If 

 so, then the chromatic matter of the deep half of the first maturation 

 spindle has been reorganized into a nucleus with a definite membrane, 

 the chromatin having become diffused as in the typical resting nucleus. 

 The radiations are perhaps the first indication of the second maturation 

 spindle. 



