THE VITAL PROPERTIES OF THE CELL 269 



Daring the retrogressive metamorphosis of the chief nucleus, 

 the small paranucleus undergoes mosfc important changes, which 

 always recur in the same manner, and which may be compared to 

 the phenomena of maturation and fertilisation seen in animal eggs. 

 It enlarges itself by taking up fluid from the protoplasm, its con- 

 tents assume a filiform appearance, until finally it transforms 

 itself into a little spindle (Fig. 148 J, nk). This spindle divides 

 into two parts, which soon develop into two new spindles ; these 

 in their turn become constricted and divide into two, so that 

 finally four spindles, which have developed out of the paranucleus, 

 are present in the neighbourhood of the main nucleus, which is 

 undergoing transformation (Fig. 148 II, 14, 58). 



During the further course of development, three of these four 

 paranuclear spindles disintegrate (III, 2, 3, 4, 6, 7, 8). They 

 become transformed into globules, which finally cannot be dis- 

 tinguished from the segments of the chief nucleus, whose fate 

 they share. They strikingly recall the formation of the pole cells 

 during the maturing of animal eggs, and in consequence have been 

 compared to them by many investigators. 



The fourth or chief spindle alone persists (II, 1 and 5) ; it takes 

 part in the process of fertilisation, and serves as the foundation 

 for the new formation of the whole nuclear apparatus in the body 

 of the Infusorian. Which of these four spindles, derived from 

 the original paranucleus, eventually becomes the chief spindle, 

 depends, according to Maupas, solely and entirely upon its position. 

 They are all four precisely alike as regards structure. The one 

 which happens to be nearest to the above-mentioned zone of ir- 

 regular thickening becomes the chief spindle (II, 1 and 5). Here 

 it places itself at right angles to the surface of the body, extends 

 itself longitudinally, and again divides into two (III, It0, 1m; 

 5w, 5m). 



Each of the halves contains apparently only about half as many 

 spindle fibrils, and half as many chromatic elements as one of the 

 earlier spindles. According to the observations made by Richard 

 Hertwig, during the division of the chief spindle the number of 

 spindle fibrils has been reduced to one half, a process similar to 

 that occurring in the nuclei of animal and plant sexual cells. 

 Hence these very characteristic nuclei play the same part as those 

 of ova and spermatozoa, and may be distinguished as male and 

 female, or as migratory and stationary nuclei. 



Further, which of the two nuclei is to be migratory and which 



