72 KARYOKINESIS. 



which may be scattered through the cell, or aggregated into a sphere around the 

 centrosorae. (2) In karyokinesis it divides, following the division of the centrosome, 

 and it forms the achromatic spindle and the polar astral systems, its granules 

 being transformed into fibres. (3) After karyokinesis its fibres are again resolved 

 into granules which are withdrawn into the spheres. (4) It is a persistent cell 

 element. 



The many points of resemblance between this substance and the " sphere sub- 

 stance" of Crepidula must be at once apparent; the most important points of dif- 

 ference are that in Crepidtda and other gasteropods this substance does not divide 

 with the division of the centrosome and is not a self perpetuating cell element. It 

 is a specific substance, temporarily distinct from other cell elements; it arises anew 

 in each cell generation ; it forms a part of the spindle and asters ; at the close of 

 karyokinesis it is withdrawn into a sphere surrounding the centrosome, and when 

 the intial spindle moves out of the sphere, the latter slowly disintegrates and disap- 

 pears in the general cytoplasm. 



Boveri held that the archoplasm sphere was largest in the prophase and then 

 diminished in size as rays were formed out of it. Zeigler, Kostanecki and Seid- 

 lecki find that the reverse is the case, viz., that the granular mass increases as the 

 rays increase and decreases with them. In all the gasteropods which I have studied 

 with reference to this point, this substance is smallest in quantity at the beginning 

 of karyokinesis and continually increases as division advances. 



If regard be had to the exact definition of archoplasm which Boveri gave, then 

 this sphere substance cannot properly be called archoplasm. However it sufficiently 

 resembles the archoplasm in location and general characteristics to warrant the 

 belief that it corresponds to the substance observed by Boveri, if not to his definition 

 of that substance. 



A specific substance, at least temporarily distinct from the general protoplasm 

 of the cell has been found in astral and karyokinetic figures by almost all recent 

 writers ; cf. Kinoplasm (Strasburger), Ei'gastoplasm (Prenant), Cyanoplasm (Mor- 

 gan), Archoplasm (Wilson, Griffin, Foot and many others). The whole appearance 

 of a karyokinetic figure, its definite form, separation from the surrounding cytoplasm, 

 staining reactions, all show that we are here dealing with a substance which is 

 specifically different from the general cytoplasm. The physiological relations of 

 the amphiaster to the cell body, no less than its morphological characteristics lead 

 to the same conclusion. On the other hand the evidence both from observation and 

 experiment now renders it extremely probable that this specific substance is a tem- 

 porary differentiation of the cell- and nuclear-plasm which may again be transformed 

 into the general protoplasm ; in short it is not self propagating and absolutely con- 

 tinuous. 



Those who have studied the eggs of Ascaris can scarcely doubt that the sub- 

 stance which Boveri described in that animal under the name of Archoplasm is 

 homologous with the specific substance found in the astral and karyokinetic figures 

 of many other organisms, and if this be the case it seems to me that the name given 



