THE SEGMENTATION OF THE OVUM. 



75 



The delicate connective filaments usually visible between the two halves 

 of the nuclear plate would seeni from Strasburger's latest observations 

 (no. 104) to be derived from the nuclear substance between the striae of the 

 spindle, and to become eventually reabsorbed into the newly-formed nuclei. 



We are it appears to me still in complete ignorance as to the 

 physical causes of segmentation. The view that the nucleus is 

 a single centre of attraction, and that by its division the centre 

 of attraction becomes double and thereby causes division, appears 

 to be quite untenable. The description already given of the 

 phenomena of segmentation is in itself sufficient to refute this 

 view. Nor is it in the least proved by the fact (shewn by Hallez) 

 that the plane of division of the cell always bears a definite relation 

 to the direction of the axis of the nucleus. 



The arguments by which Kleinenberg (93) attempted to demon- 

 strate that cell division was a phenomenon caused by alterations in 

 the molecular cohesion of the protoplasm of the ovum still in my 

 opinion hold good, but recent discoveries as to the changes which 

 take place in the nucleus during division probably indicate that the 

 molecular changes which take place in the cohesion of the protoplasm 

 are closely related to, and possibly caused by, those in the nucleus. These 

 alternations of cohesion are produced by a series of molecular changes, 

 the external indications of which are to be found in the visible altera- 

 tions in the constitution of the body of the cell and of the nucleus prior 

 to division. 



BIBLIOGRAPHY. 



In addition to the papers cited in the last Chapter, vide 



(101) W. Flernmiug. "Beitrage z. Keoutniss d. Zelle u. ihrer Lebenserschei- 

 nuugeu." Archiv f. viikr. Anat., Vol. xvi.,1878. 



(102) E. Klein. "Observations on the glandular epithelium and division of nuclei 

 in the skin of the Newt." Quart. J. of Mlcr. Science, Vol. xix. , 1879. 



(103) Peremeschko. "Ueber d. Theiluug d. thierischeu Zelleii." Archie f. mi kr. 

 Anat., Vol. xvi., 1878. 



(104) E. Strasburger. "Ueber eiu z. Demonstration geeignetes Zelltheilungs- 

 Object." Sitz. d. Jenaischen Gesell.f. Med. u. Naturwiss., July 18, 1879. 



External Features of Segmentation. 

 In the simplest known type of segmentation the ovum first of 



Fiu. 38. VARIOUS STAGES IN PROCESS OF SEGMENTATION. (After Gegenbaur.) 



all divides into two, then four, eight, sixteen, thirty-two, sixty-four, 

 etc. cells (fig. 38). These cells so long as they are fairly large 



