THE ARCHOPLASMIC STRUCT C RES 323 



In its more restricted form, however, the urchoplasm or kinopiasm 

 hypothesis is of high interest as indicating a common element in the 

 origin and function of the mitotic fibrilkie, the centrosome and mid- 

 body, and the contractile substances of cilia, flagella, and muscle- 

 fibres. The main interest of the hypothesis seems to me to lie in the 

 definite genetic relations that have been traced between the archo- 

 plasmic structures of successive cell-generations (as is most clearly 

 shown in the phenomena of maturation and fertilization). It has 

 been pointed out at various places in the preceding chapters ^ how 

 many apparently contradictory phenomena in cell-division, fertiliza- 

 tion, and related processes can be brought into relation with one 

 another under the assumption of a specific substance, carried by the 

 centrosome or less definitely localized, which gives the stimulus to 

 division, which is concerned in the formation of the mitotic figure 

 and of contractile elements, and which may be transmitted from cell 

 to cell without loss of its specific character. There seems, however, 

 to be clear evidence that such substance (or substances), if it exists, 

 is not to be regarded as being necessarily a permanent constituent of 

 the cell, but only as a phase, more or less persistent, in the general 

 metabolic transformation of the cell-substance.^ 



3. The Attraction-spJiere 



As originally used by Van Beneden ^ the term attraction-spJicrc was 

 applied (in Ascains^ to the central mass of the aster surrounding the 

 " corpuscule central " and consisting of medullary and cortical zones, 

 as already described (p. 310). The cortical zone is bounded by a di.s- 

 tinct circle of microsomes from which the astral rays proceed ; and at 

 the close of cell-division the rays were stated to fade away, leaving 

 only the attraction-sphere, which, like the centrosome, was regarded 

 as a permanent cell-organ. Later researches have conclusively shown 

 that the attraction-sphere cannot be regarded as a permanent organ, 

 since in many cases it disintegrates and disappears. This occurs, for 

 example, in the early prophases of mitosis in the testis-cells of the sala- 

 mander,^ where the sphere breaks up and scatters through the cell as 

 the new amphiaster forms (Fig. 27). A very interesting ca.se of this 

 kind occurs in the cleavage of the ovum in Crcpidiila, as described by 

 Conklin ('99). The spheres here persist for a considerable period 

 after division (Fig. 192), but have no direct relation to those of the 

 ensuing division, finally disappearing /// situ. The new spheres are 

 formed about the centrosomes, which Conklin believes to migrate 

 out of the old spheres (somewhat as occurs in the spermatid, p. iC7)to 

 their new position. The interesting point here is that the old sphere 



1 (7: pp. Ill, 215. 2Qrp. 171. 8'Sj, p. 548. 



* Druner, '95, Rawitz, '96, Meves, '96, 



