36 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
plasm, and three orders of limiting membrane; even the endoplasm 
shows a hint of two zones. As to the centrosomes (chap. 8.), they vary 
in number up to 135 ! there is a constant central group and there are 
several smaller groups. The ninth chapter is full of details as to the 
fine structure of the protoplasm in giant cells ; then follow chapters on 
the development of the cells — their early stages, their mitoses, their 
direct division, and on their degeneration — which shows (a) forms 
described by Arnold, with chromatolytic nuclei, (b) forms without proto- 
plasm, (c) complete disruption of nuclei. 
The thirteenth chapter, which begins the theoretical portion, dis- 
cusses the general conception of a centrosome. Central corpuscles are 
sharply defined solid granules of very small size, specifically stainable 
by iron-hsematoxylin. They have the power of assimilating, of growing, 
and of multiplying by budding. They show a marked tendency to form 
groups, and the members of a group are united by a substance formed 
during multiplication. Singly or as a group they unite the origins 
of the threads of a centered system. 
The next chapter is devoted to a general discussion of the astrosphere. 
This is a topographical conception. The astrosphere or attractive 
sphere is no definite organ ; it owes its origin to the fact that the inner 
ends of the threads of a centered system are secondarily defined off from 
the rest of the cell by the appearance of a granular zone. 
As to the archoplasm (chap. 14), it is no substance of specific 
quality, as Boveri maintains, but a part of the cyto-mitome. The 
alleged ubiquity of centrosomes is the subject of the next chapter. This 
was a bold prophecy on the part of van Beneden and Boveri, but it 
seems justifiable. The centrosome appears to be constant in all cells 
which are still able to divide. But the author is careful to notice that 
there is apparently a formation of centrosomata de novo in many cells, 
and that the centrosome is apparently absent from cells of the adult 
body which are incapable of division (ganglion-cells). The sixteenth 
chapter is concerned with showing that there is a specific substance in 
the centrosomes which does not occur in other parts of the cell. As to 
the physiological role of the centrosome (chap. 17), whether it be the 
central insertion-point of a system of contractile fibrils, or whether it is 
a dynamic centre controlling its surroundings, Heidenhain is cautious, 
but the former is the alternative which he supports. 
The origin of the centrosome (chap. 18) is then discussed. It is a 
question of topography mainly, for there is no essential difference 
between nuclear and cytoplasmic substance. The author’s view is that 
the macronucleus of Infusoria represents the nucleus of Metazoa, that the 
chromatin substance of the micronucleus has disappeared from the cells 
of Metazoa, that the achromatin substance surrounding the centrosome 
in the microcentrum of lymphocytes corresponds to the achromatin sub- 
stance of the micronucleus of Infusoria, both giving origin to spindles ; 
the macronucleus has come to be represented by the part transporting 
the chromosomes ; the centrosomes are polar differentiations of the micro- 
nuclear spindle. Finally (chaps. 19 and 20) the author discusses the 
various hypotheses of cell-polarity (Flemming’s, Rabl’s, van Beneden’s), 
but we refrain from following him. While we have stated his chief 
conclusions, it is self-evident that we have been forced to leave un- 
touched much that is important in this monumental memoir. 
