70 ^SUMMARY. 



These conclusions tally very satisfactorily with the view adopted 

 in the Introduction, that impregnation amongst the Metazoa was 

 derived from the process of conjugation amongst the Protozoa. 



Summary. 



In what may probably be regarded as a normal case the 

 following series of events accompanies the maturation and impreg- 

 nation of an ovum : 



(1) Transportation of the germinal vesicle to the surface of the 



egg- 



2) Absorption of the membrane of the germinal vesicle and 

 metamorphosis of the germinal spot and nuclear reticulum. 



(3) Assumption of a spindle character by the remains of the ger- 

 minal vesicle, these remains being probably in part formed from the 

 germinal spot. 



(4) Entrance of one end of the spindle into a protoplasmic 

 prominence at the surface of the egg. 



(5) Division of the spindle into two halves, one remaining in 

 the egg, the other in the prominence ; the prominence becoming 

 at the same time nearly constricted off from the egg as a polar 

 cell. 



(6) Formation of a second polar cell in the same manner as the 

 first, part of the spindle still remaining in the egg. 



(7) Conversion of the part of the spindle remaining in the egg 

 into a nucleus the female pronucleus. 



(8) Transportation of the female pronucleus towards the centre 

 of the egg. 



(9) Entrance of one spermatozoon into the egg. 



(10) Conversion of the head of the spermatozoon into a nucleus 

 the male pronucleus. 



(11) Appearance of radial stria3 round the male pronucleus, 

 which gradually travels towards the female pronucleus. 



(12) Fusion of male and female pronuclei to form the first 

 segmentation nucleus. 



(76) Auerbach. Organoloijische Studien, Heft 2. Breslau, 1874. 



(77) Barnbeke. "Eecherches s. Embryologie des Batraciens." Bull.de VAcad. 

 royale de Belriique, 2me ser., T. LXI., 1876. 



(78) E. Van Beneden. "La Maturation de 1'CEuf des Mammiferes." Bull, de 

 VAcad. royale de Belyique, 2ine ser., T. XL. No. 12, 1875. 



(79) Idem. " Contributions a 1'Histoire de la Vesicule Germiuative, &c." Bull.de 

 VAcad. royale de Belyique, 2rne ser., T. XLI. No. 1, 1876. 



(80) 0. Btitschli. Eizelle, Zelltheilung, und Conjugation der Infusoricn. Frank- 

 furt, 1876. 



(81) F. M. Balfour. "On the Phenomena accompanying the Maturation and 

 Impregnation of the Ovum." Quart. J. of Micros. Science, Vol. xvm., 1878. 



(82) Calberla. "BefruchtungsvorgangheimEi von Petromyzon Planeri." Zelt. 

 f. wiss. Zool., Vol. xxx. 



(83) W. Fl em ruing. " Studien in d. Entwickelungsgeschichte der Najadeu." Sit:. 

 d. k. Akad. Wien, B. LXXI., 1875. 



(84) H. Fol. "Die erste Entwickeluug des Geryouideneies." Jenaische Zeitschrift, 

 Vol. vii., 1873. 



