204 First Maturation Spindle of Allolobopliora Foctida 



satisfactory data as to the origin of the centriolcs of the first maturation 

 spindle. 



i\[eves", '02, observations as to the constancy in size of the centrioles, 

 regardless of the size of the cells are supported by this egg. There is 

 an insignificant difference in size between the centrioles at the metaphase 

 of the first maturation spindle (Photos. 26, Plate II, 91, 92a and b, 

 Plate V, 99, 100, 101, 102 and 106, Plate VI), the second matura- 

 tion spindle (Photos. 103, 104, 105, 108 and 109), the first, second 

 (Photo. 110), and third cleavage spindles (Photo. 107, Plate VI). ' 

 There are often exceptions to this rule, but in many of these cases the 

 cause is obviously overstaining (Photo. 83, Plate V), for centrioles 

 that we have seen or photographed in unstained preparations, as a rule, 

 show no more variation in size than can be accounted for by different 

 fixation, or individual variations. Photos. 92a and b, Plate V, show 

 also a similarity in size of the centrioles of the peripheral and inner 

 poles of the first maturation si3indle. There is, however, a dissimilarity 

 in size between the centrioles of the prophases and metaphases of the 

 first maturation spindle, the former being smaller, indicating that the 

 centriole passes through stages of growth (comj)are the centrioles of 

 Photos. 81, 82, 84 and S6, Plate V, with those of the metaphase, Plate 

 VI). That centrioles are sometimes found out of the center of the 

 sphere is probably due to fixation, for if fixation can produce such marked 

 variations of cytoplasmic and nuclear structures as demonstrated in these 

 photographs, it is indeed remarkable that the central position of the 

 centriole is maintained as constantly as v^e find it in these eggs. 



The first maturation spindle can be readily identified in the living egg. 

 In Photos. 125, 128, 129 and 130, Plate IX, we see spindles that have 

 retained their form after the contents of a living egg has been pressed 

 out of its membrane and allowed to dry quickly on a slide. In such 

 preparations we have found no trace of a centriole, but we cannot give 

 much weight to this evidence for in all fixed material, both stained and 

 unstained, a centriole is invariably present at each pole. Unstained cen- 

 trioles are demonstrated in the spindles of Photos. 91 and 99, Plates V 

 and VI, and stained centrioles in the spindles of Photos. 26, Plate II, 

 92a and b, Plate V, and Photos. 100 to 110, Plate VI. 



Photos. 84 to 89, Plate V, suggest that a large part of the spindle is 

 formed of achromatic nucleoplasm. In Photos. 86 to 89 a part of the 

 membrane of the germinal vesicle is still seen and the nucleoplasm within 



«The magnification of Photos. 99, 102, 108 and 110 is 710 diameters, and 

 Photos. 26 and 109, 1100 diameters. All the others are 1000 diameters. 



