ie 
+1894] A ttraction-Spheres and Centrosomes. | 449 
by the cytoplasmic threads of the polar radiations. Thus an 
important part of the karyokinetic process would take place 
_ outside of the nucleus. Van Beneden also made the general- 
ition that the spheres with their central bodies were of 
quite general distribution in both animal and vegetable cells. 
Heidenhain (153) considers that the attraction-sphere is 
_ fot a constant characteristic of the cell but, as is the case in 
leucocytes, it is present only during the resting period of the 
cell, and not during the process of karyokinesis; thus the at- 
_ Mfaction-sphere is not considered to be an organ in the exact 
meaning of the word. He considers that the ‘‘microcentrum” 
(centrosome with its envelopes) of the higher organisms cor- 
Tsponds to the paranucleus of the protozoa while the nucleus 
‘orresponds to the macronucleus. He gives some important 
discussions on the physiological réle of centrosomes and the 
law of their position, together with other theoretical views, 
but since they are beyond the scope of this paper they will 
hot be considered here. 
Biirger’s (2) views are the following: He thinks that the 
bodies are not permanent organs, but that they are simply 
due to certain mechanical processes; that the central body is 
lot the cause but the result of polar attraction. That is, he 
thinks the microsomes are attracted toward the center of the 
Polar fegion from the periphery, and since they are solid 
bodies, if they are attracted equally from all sides, they form 
‘hollow Sphere which is the attraction-sphere. aw 
we tase (31) has advanced an hypothesis somewhat similar. 
i thinks that the centrosome is simply a large microsome 
"med at the point where the greatest number of cytoplasmic fil- 
aeutsmect; that a barrel-shaped pindlet inde- 
- €nt microsomes at each pole instead of one centrosome. But 
em €xplanation, as well as that of Biirger, corresponds igre 
i the observed facts that it seems entirely io atagee 
bs Could not be a reasonable rere ie 
i: * Seen beside the resting nucleus by Guignar lan ae 
wt the four spherical bodies, which can be so easily seen 
| hy *takinesis in cells of the ovary of Lilium and other 
- Plants ) 
For the filamentary structure of cytoplasm has not yet been 
‘Mic Sastrated in plants; and if the centrosomes are only aie 
ea omes, then the spindle must be divided into halves to 
MSduce the two centers at the poles, or else there must be a 
