Maturation and Fertilization in Theridiura. 243 



this particular stage though from the counts made at later stages 

 the number must be 12. The spindle is of considerable length, ex- 

 tending radially through the thickness of the columnar yolk layer. 

 I have been unable to distinguish any structural polarity of 

 the egg. After oviposition the eggs are rarely spherical, but are 

 usually slightly monaxonic and in this case one may distinguish for 

 convenience two poles and an equator. Of twenty polar spindles 

 examined with reference to their position, 11 were at or near one 

 of the poles and 9 at or near the equator. This would show either 

 that the polar bodies can be formed at any point, or that the axes 

 of the egg have no constant relation to the points where the polar 

 spindles occur. Also there were no means of determining whether 

 the sperm enters at the point where the polar bodies are formed, 

 unless indeed the body x of Fig. 1 should be demonstrated to be a 

 sperm, in which case the question could be answered in the affirmative. 

 Often the columnar yolk layer appears to be thicker at one point 

 than at others, but this may be due to the action of the fixatives. 



IV. Stage of the Second Polar Spindle. 



Up to fifteen minutes after oviposition the spindle continues in 

 the anaphase of the first maturation mitosis, but becomes more 

 curved or bent. Fig. 9 shows the outer plate of chromosomes at 

 5 minutes after oviposition. At 20 — 25 minutes the connective fibres 

 have ruptured and the first polar body is left at the surface 

 separated from the second polar spindle below it. 



The chromosomes of the first polar body lie at the surface in 

 a thickening of the superficial cytoplasm, but this mass does not 

 project above the surface of the egg nor does it become clearl}' 

 demarcated by a cell membrane from the egg, for at the most the 

 boundary in very faint (Fig. 12); that is, this polar body does not 

 appear to become cut oif from the egg. Soon it developes a spindle 

 (Figs. 11 — 14) and its chromosomes become arranged in one plane; 

 this spindle is exactly like the second polar spindle, and on pole 

 views of it 12 chromosomes can be counted (Fig. 10). This condition 

 is found in stages from twenty-five minutes to an hour or even 

 later. The chromosomes are dyads and undergo a division the be- 

 ginning of which is illustrated in Fig. 13 (age of one and a half 

 hours) and a later anaphase in Fig. 21. After the age of two hours 

 the first polar body was not found. 



The second polar spindle forms in all cases in the immediate 



