CELL-ORGANS OF SEA-URCHIN EGG 591 



matic daughter nucleus. The achromatic daughter nuclei exert 

 an attraction upon the basophilic substance, which again is found 

 in the cytoplasm. Radiations surround the nuclei, and a division 

 of cytoplasm takes place in the region, where the radii of the 

 astrospheres meet. In this region the attraction, exerted by the 

 nuclei, is displayed in two opposite directions. 



9. A few statements of more general value may be allowed. It 

 seems on the basis of the present study, that if a given structure 

 appears regularly at definite stages of cell mitosis, it is due to the 

 fact, that the physico-chemical process of life is composed of 

 cycles, and that the final stages of cycles become starting points 

 I'jr other similar cycles. Every step of a cycle is exhibited in our 

 preparations by the regular appearance of morphological struc- 

 tures (cell organs), which as such are all temporary. They re- 

 appear regularly as result of development of analogous physico- 

 chemical processes, which underlie the life history of the cell. 

 Their changes are easily appreciable in those stages of develop- 

 ment of living substance, which are separated by lengths of time, 

 and appear as different specimens of the organic world. The 

 differences exhibited by the most essential cell organs are in this 

 case easily demonstrated by our preparations. The study of 

 the gradual differentiation of cell organs during ontogenesis 

 offers great difficulty and only further investigations may throw 

 light upon this problem. 



It gives me great pleasure to express my thanks to Prof. C. 

 E. McClung for valuable advice and for reading the test. 



LITERATURE CITED. 



Bergh, R. S. 1889 Recherches sur les noyaiix de I'Urostyla. Arch. Biol., 9. 



BovERi, T. Zellstudien I, II, III, IV, V. 



1887 Ueber den Anteil des Spermatozoons an der Teilung des Eies. 

 Sitzungsber. d. Ges. f. Morph. u. Phys. Mlinchen, Bd. 3. 

 1895 Ueber das Verhalten des Centrosoms bei der Befruchtung des 

 Seeigeleies . . . . Verb. d. Phys. Med. Ges. zu. Wiirzburg, 

 N. F., Bd. 29. 



BuTSCHLi, O. 1896 Weitere Ausfiihrungen iiber den Bau der Cyanophyceen 

 (flagel) u. Bakterien, Leipzig. 



CALKI^s, G. N. 1898 The phylogenetic significance of certain protozoan nu- 

 clei. Ann. N. Y. Acedem. Sci., 11, 16. 



JOU fAL OF MORPHOLOGY, VOL. 27, NO. 3 



