1 86 CALIFOKNJA ACADEMY OF SCIENCES. [Pkoc. .^n Skk. 



EXPLANATION OF PLATE XXXV. 



Fig. 13. Here we see a characteristic multipolar spindle, the fibres straight 

 and definite, and the cones terminating in sharp points. We 

 also see fibres with fi-ee ends projecting from the apices of the 

 cones. These eventually become the mantle-fibres in the 

 mature spindle. It will also be noticed that the chromosomes 

 have taken up a more central position. 



Fig. 14. This figure shows that certain of the poles Iiave approached each 

 other and we have the indication of a bipolar spindle. The 

 mantle-fibres have also grown to a considerable length. 



Fig. 15. This figure shows the mature bipolar spindle. The chromosomes 

 lie in the ecjuatorial plate. The mantle-fibres have developed 

 to an extraordinary length ; those from one pole cross those 

 from the opposite pole. The mantle-fibres, although very long, 

 do not extend beyond the perikaryoplasm. The contractile 

 fibres, which are connected with the chromosomes, are plainly 

 compound in nature. There are also continuous fibres to be 

 seen which extend from pole to pole uninterrupted. 



Fig. 16. This stage is a little later than that shown in fig. 15. The chro- 

 mosomes have separated and have commenced t(j move 

 towards the poles. Tiie poles of the spindle terminate in sharp 

 points. The manlie-fibres have reached their maximum 

 development. 



Fig. 17. By the contraction of the contractile fibres the chromosomes have 

 been drawn toward the poles. The mantle-fibres now appear 

 to be more divergent from their respective poles. 



Fig. 18. The chromosomes have now reached the poles. The mantle- 

 fibres have lost their straight appearance and hang loosely 

 alongside of the remaining continuous fibres. 



