240 THE CELL 



the contractive action of the spindle fiber to which it is attached ; and 

 one daughter- segment passes to each pole {anaphase stage). Each of 

 the two groups of daughter- segments very soon becomes surrounded by 

 a new membrane, the chromosomes gradually fuse end to end, the 

 nucleolus reappears, and at length two resting nuclei are produced 

 similar in every respect to the parent nucleus [telophase stage). 

 Meanwhile each spindle fiber becomes swollen at the equator, thus 

 producing a series of dots all arranged in one plane. These at length 

 fuse, forming a delicate transverse cell-membrane, which by the pe- 

 ripheral expansion of the spindle at length reaches the lateral walls, and 

 cell-division is thus complete. This process of indirect nuclear 

 division is one of the most wonderful phenomena yet discovered in 

 organic development, not only on account of its intricacy and beauty, 

 but also because it has been found that hereditary characteristics are 

 in all probability transmitted solely through the chromosomes. The 

 longitudinal division and separation seem to be for the purpose of 

 insuring equal apportionment of the hereditary substance to each 

 daughter-nucleus. The subject, however, is still in its infancy, and 

 authors disagree both as to details and as to theoretical considerations. 



Note on Scope, Apparatus, and Methods. — The work outlined 

 in Part III is sulficient, if well done, to occupy one period of the 

 pupil's time each school day for six weeks. These chapters are 

 intended only as laboratory guides. The pupil should work out each 

 structure or part for himself before taking up the succeeding subject. 

 The work in this Part deals with only the elements of the subject, but 

 it is as much as the high school pupil can hope to take up with profit. 



Apparatus. — The apparatus necessary for the work outlined in 

 these chapters on histology may be obtained from dealers in micro- 

 scopes and laboratory supplies at a low figure. Schools should obtain 

 catalogues from the following and other reliable dealers: 



Bausch & Lomb Optical Co., Rochester, N. Y. 



Eimer & Amend, New York. 



The Franklin Educational Co., Boston. 



Queen & Co., Philadelphia. 



Richards & Co., Chicago and New York. 



Spencer Lens Co., Buffalo. 



Williams, Brown & Earle, Philadelphia. 



Geneva Optical Co., Chicago. 



Whitall, Tatum & Co., New York. 



Chas. Lentz & Sons, Philadelphia. 



Richard Kny & Co., New York. 



Cambridge Botanical Supply Co., Cambridge, Mass. 



