222 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the karyokinetic figure. The entire achromatic division figure is due to 

 the cell-substance. Parallel with the phases of the nuclei there are 

 phases of the protoplasm, which finally lead to the well-known appear- 

 ance of the achromatic nuclear spindle with the two polar suns. It was 

 Boveri's merit in 1887 to point this out for the first time; van Beneden 

 and Neyt have since followed him. The cell-substance, according to 

 Boveri, consists of a homogeneous matrix and a fine network, between 

 the meshes of which lie yolk-corpuscles, irregular granules, and a specific 

 granular or filamentar substance. This last alone has an active role in 

 the process of division. For it, Boveri proposes the new title of archo- 

 plasma. It is demonstrable by a certain action of picro-acetic acid, of 

 which the author does not give the details, but which leaves the nucleus 

 and the archoplasma alone distinct. It is unfortunately difiicult, within 

 the limits of a report, to relate how Boveri has followed the modifications 

 of the archoplasma in relation, for instance, to the " central corpuscle " 

 or " centrosoma " of van Beneden and Neyt, or other phenomena of 

 division. " The centrosoma exercises upon the archoplasma contained 

 in the cell an attraction of this sort, that round itself as centre it con- 

 tracts the above substance into a dense granular sphere." The division 

 of the originally single mass of archoplasma into two spheres fs the 

 result of the presence and opposition of two equally strong centrosomata. 

 It is probable that the sperm brings with it a centrosoma which divides. 

 When the two are adjacent, their attractions only modify the archo- 

 plasma slightly from the spherical form. As they go apart, the more 

 marked does the constriction of the archoplasma become. Dr. Boveri 

 draws a sharp contrast between the polar and the segmentation spindles, 

 which turn out to be extremely different so far as their achromatin 

 constituents are concerned. 



(5) The origin and division of the first segmentation spindle. — In the 

 first part of this chapter the relations between the archoplasmic spheres 

 and the nuclear elements are followed from their beginning to their 

 perfected result. 



The spindle-formation begins with the radiate metamorphosis of the 

 two archoplasmic spheres. Radiating fibrils, growing at the expense 

 of the central granular portion, meet and attach themselves to the 

 chromatin elements. Is this by chance or by attraction, is a question 

 hard to answer, but probabilities are in favour of the former. All the 

 threads which connect one sphere with a chromatin element attach 

 themselves exclusively to the one narrow surface; all those from the 

 other sphere likewise attach themselves to the other narrow surface. 

 Each daughter-element within a mother-element admits of the attach- 

 ment of the threads from one pole only. The fibrils thus attached to a 

 chromatic loop seek to contract, and this contraction may go so far that 

 the length of the threads aj^proaches the radius of the original sphere. 

 The contraction brings about a corresponding approximation between 

 the centrosoma and the point of the loop with which the fibrils are 

 associated. These archoplasmic threads are genuinely like muscle- 

 fibrils. " The movement of the elements is solely and wholly the result 

 of the contraction of the attached fibrils, and the final arrangement of 

 the above into an ' equatorial plate ' is the result of the equal action 

 of the two archoplasmic spheres exerted through the said fibrils." 



In a later portion of the chapter the author enters into detail in 

 regard to the stage with the equatorial plate. The stage has very definite 



