MATURATION AND IMPREGNATION OF THE OVUM. 131 



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

 nucleus — the male pronucleus. 



(11) Appearance of radial striae round the male pronucleus 

 which gradually travels towards female pronucleus. 



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

 segmentation nucleus. 



List of important recent Publications on the Maturation and 

 Impregnation of the Ovum. 



1. Auerbach. Organologische Studien, Heft 2. 



2. Bambeke. Reclierclies s. Embrjologie des Batraciens. Bull, de 

 I'Acad. royale de Belgique, 2me sen, t. Ixi, 1876. 



3. E. Van Beneden. La Maturation de I'CEuf des Mammiferes. Bull, de 

 I'Acad. royale de Belgique, 2me ser., t. xl, no. 12, 1875. 



4. Idem. Contributions a I'Histoire de la Vesicule Germinative, &c. 

 Bull, de I'Acad. royale de Belgique, 2me ser., t. xli, no. 1, 1876. 



5. Biitschli. Eizelle, Zelltheilung, und Conjugation der Infusorien. 



6. Flemming. Studien in d. Eutwickelungsgeschichte der Najaden. 

 Sitz. d. k. Akad. Wien, B. Ixxi, 1875. 



7. Fol. Die erste Entwickelung des Geryonideneies. Jenaische Zeit- 

 schrift, vol. vii. 



8. Idem. Sur le Developpement des Pteropodes. Archives de Zoologie 

 Experinientale et Geu^rale, vol. iv and v. 



9. Idem. Sur le Commencement del'Henogenie. Archives des Sciences 

 Physiques et Naturelles. Geneve, 1877. 



10. Giard. Note sur les premiers phenomenes du developpement de 

 rOursin. 1877. 



11. Eertwig, Oscar. Beit, z, Kentniss d. Bildung, &c., d. thier. Eies. 

 Morphologische Jahrbuch, Bd. i. 



12. Idem. Ibid. Morphologische Jahrbuch, Bd. iii, Heft 1. 



13. Idem. Weitere Beitrage, &c. Morphologische Jahrbuch, Bd. iii, 

 Heft 3. 



14. Kleinenberg. Hydra. Leipzig, 1872. 



15. Oellacher, J. Beitrage zur Geschichte des Keimblaschens im 

 Wirbelthiereie. Archiv. f. micr. Anat., Bd. viii. 



16. Selenka. Befruchtung u. Theilung des Eies von Toxopneustes 

 variegatus (Vorlaufige Mittheilung). Erlangen, 1877. 



17. Slrasburger. Ueber Zellbildung u. Zelltheilung. Jena, 1876. 



18. Idem, Ueber Befruchtung u. Zelltheilung Jena. 1878. 



19. R. Greeff. tJb. d. Bau u. d. Entwickelung d. Echinodermen. Sitzun. 

 der Gesellschaft z. Beforderung d. Gasammten Naturwiss z. Marburg, 

 No. 5. 1876. 



Postscript. — Two important memoirs have appeared since this paper was 

 in type. One of these by Hertwig, ' Morphologische Jahrbuch,' Bd. iv, 

 contains a full account with illustrations of what was briefly narrated in 

 his previous paper (13) ; the other by Calberla, 'Der Befruchtuugsvorgang 

 beim Ei von Fetromyzon Planeri.^ 'Zeit. fiir Wiss. Zool.,' Bd. xxx, shows that 

 the superficial layer of the egg is formed by a coating of protoplasm free 

 from yolk-spheres, which at one part is continued inwards as a column, 

 and contains the germinal vesicle. The surface of this column is in contact 

 with a micropyle in the egg-membrane. Impregnation is effected by the 

 entrance of the liead of a single spermatozoon (the tail remaining outside) 

 through the micropyle, and then along the column of clear protoplasm to 

 the female pronucleus. 



