54 THE MATURATION OF THE EGG OF THE MOUSE. 



the form of short rounded rods such as Sobotta shows in his (1895) 

 fig. 10a. But Sobotta, as we think, and as he would probably now admit, 

 made a mistake in supposing that his figures 10 and 10a represented the 

 first maturation spindle. The egg in question was taken from the ovi- 

 duct, and therefore exhibits the second maturation spindle. It may be 

 noted, in passing, that by some strange slip of the pen Sobotta (1895, 

 p. 91) describes his fig. 10c as representing the beginning of metakinesis 

 instead of an advanced anaphase. In his more recent paper he (Sobotta, 

 1907, pp. 508-511, fig. 2, fig. 3) has figured two spindles which may 

 more properly be said to exhibit an equatorial plate, though even here 

 the chromosomes do not assume that rigid, plate-like arrangement which 

 characterizes the equatorial plate in many other animals and also that 

 of the second maturation spindle in the mouse. This equatorial-plate, 

 or monaster, stage of the first spindle is distinguished (Sobotta, 1895, 

 pp. 508-511) from the prophase by the possession of smoother and 

 straighter spindle fibers and by the predominance of chromosomes 

 having a large one-sided protuberance. There is no disagreement among 

 authors concerning the orientation of the chromosomes on the spindle 

 nor concerning the fact that they vary in size. But as to the number 

 of chromosomes, there is a wide difference of opinion. Tafani and the 

 present writers count 20. Sobotta — whose view has been accepted by 

 all subsequent investigators, apparently under the influence of the large 

 amount of his material— maintained in 1895 that there were 12 chromo- 

 somes; but recently, stimulated by Dr. J. A. Murray to a reexamination 

 of his material, he has changed his opinion, and in two papers (1907, p. 

 512; 1908, pp. 248, 259) has stated that the number is certainly 16. 

 Holl (1893, P- 284) argued that since at an earlier stage there were 24 

 chromatic balls, there should be as many loop-like chromosomes, and was 

 able to count 20; but not much weight can be given to his conclusions. 

 He admits that it was impossible to count the chromosomes accurately. 



The short account by Melissinos (1907, p. 584) is remarkably un- 

 critical. After stating that Tafani gave the number as 20, Holl as 18, 1 

 Sobotta as 12, and others as 24, he remarks that Sobotta's counting seems 

 to him the more accurate, and then proceeds to state that he can make 

 out only 8. But his figures are too diagrammatic to inspire much con- 

 fidence on the part of the reader. 



As already shown (p. 45), the number of eggs in which Sobotta could 

 possibly have counted chromosomes is really small. In 1895 (P- 4^) he 

 maintained on the strength of many successive countings of the same 

 material that the slender (second) spindle in all probability possessed 

 12 chromosomes, surely not over 14 or 15. Moreover, in the case of the 

 thicker first spindle (p. 51) there were three eggs in which he counted 



1 It is not clear how Melissinos conies to make Holl responsible for the view 

 that the mouse egg shows t8 chromosomes, unless, perchance, his eye fell on the 

 page (280) where Holl reports that Ruckert found "about 18 chromatin rods" in 

 Selachian eggs. 



