88 EDWIN G. CONKLIN 
tension at the poles of the cell. Therefore, the causes of equal 
or unequal, differential or non-differential divisions are intrinsic 
rather than extrinsic (pp. 78-81). 
26. Whenever the size, constitution or number of blastomeres 
is changed from the typical condition, subsequent cleavages come 
back to the normal form so far as this is possible. This regula- 
tion in cleavage is connected with a persistent polarity of the cell, 
which is not changed by centrifuging, and which manifests it- 
self in a definite cell axis passing through nucleus and centrosome, 
in typical movements and localizations of cell contents, and in 
reduced tension of cell membrane at the poles of the cell (pp. 
81-83). 
LITERATURE CITED 
Bautzer, F. 1908 Die Chromosomen von Strongylocentrotus lividus und Echi- 
nus microtuberculatus. Arch. f. Zellforschung, Bd. 2. 
Boveri, Tu. 1902 Ueber mehrpolige Mitosen als Mittel zur Analyse des Zell- 
kerns. Verh. d. Phys. med. Gess. Wirzburg., Bd. 35. 
1904. Ergebnisse tiber die Konstitution der chromatischen Substanz 
des Zellkerns. Jena. 
1905 Zellenstudien V. Ueber die Abhangigkeit der Kerngrésse und 
Zellenzahl der Ausgangszellen. Jena. 
1910 Ueber die Teilung centrifugierter Eier von Ascaris megalocephala. 
Arch. f. Entw. Mech., Bd. 30. 
Conkuin, E. G. 1893 The fertilization of the ovum. Woods Hole Lectures. 
Ginn and Co., Boston. 
1897 The embryology of Crepidula. Jour. Morph., vol. 13. 
1899 Protoplasmic movement as a factor in differentiation. Woods 
Hole Lectures. 
1902 Karyokinesis and cytokinesis in the maturation, fertilization 
and cleavage of Crepidula. Jour. Acad. Nat. Sciences of Philadelphia, 
vol. 12. 
1905 The organization and cell-lineage of the ascidian egg. Idem, 
vol. 13. 
1910 The effects of centrifugal force on the organization and develop- 
ment of the eggs of fresh water pulmonates. Jour. Exp. Zool., vol. 9. 
Cuitp, C. M. 1911 A study of senescence and rejuvenescence based on experi- 
ments with Planaria dorotocephala. Arch. f. Entw. Mech., Bd. 31. 
ERpDMANN, Rh. 1908 Experimentelle Untersuchung der Massenverhaltnisse 
von Plasma, Kern und Chromosomen in dem sich entwickelnden Seeige- 
lei. Arch. f. Zellforschung, Bd. 2. 
