THE VITAL PHENOMEXA OF THE CELL 203 



from the exterior, appears to me, at the least, forced. Further, in 

 my opinion, it can no longer be doubted that the connecting 



A 

 .'f'f 



FIG. 97.^ A germinal vesicle, in which a spindle is developing, taken from a newly 

 laid egg of Phyllirhoe. Acetic acid preparation (Hertwig, PI. XI., Fig. 2). B Germinal 

 vesicle from a freshly laid egg of Phyllirhoe, in which the spindle is seen in optical section. 

 Acetic acid preparation (Hertwig, PI. XI., Fig. 6). 



threads, which, in the dividing sperm-mother-cells of Ascaris, ex- 

 tend between the separating nuclear segments, are derived from 

 the liiiin framework. I was not able to observe a typical spindle 

 development in this object. 



Another point under discussion is the origin of the centrosomes. 

 These were first described and depicted at the commencement 

 of the year 1870, but they were only brought into prominence as 

 a distinct component part of the nuclear division figure by van 

 Beneden (VI. 4a), when he succeeded in differentiating them 

 clearly from their environment by means of a staining solution of 

 aniline dyes dissolved in 33 per cent, glycerine solution. Soon 

 afterwards both van Beneden and Boveri made simultaneously and 

 independently of each other (VI. 4b, 6) the important discovery, 

 that centrosomes multiply by self-division ; later on I was able to 

 verify this statement for the sperm cells of Ascaris (VI. 34-). Van 

 Beneden came to the following conclusion as a result of his 

 observations : that the centrosomes, like nuclei, are permanent 

 organs of the cell, and must therefore always occur in the proto- 

 plasm as independent forms. This view was supported to a 

 certain extent by the discoveries of Flemming (VI. 17), Solger 

 (VI. 70), and Heidenhain (II. 16), who stated that in many 

 kinds of cells, such as lymph corpuscles and pigment cells, a 

 centrosome with a radiation sphere may be demonstrated in the 

 protoplasm, even when the nucleus, which is frequently situated 

 some little distance off, is completely at rest. (See p. 56, Figs. 

 34-36.) 



