52 CHORDATA. 



investing epithelial cells, which at the same time lose their nuclei. 

 When the whole of the central ball is thus absorbed by the 

 epithelial cells, the latter become used by the winter ovum as 

 food. The winter ovum at its full development is formed of a 

 central mass of food-yolk and superficial layer of protoplasm. 



CHORDATA. 

 Urochorda. (Tunicata.) 



(58) A. Kowalevsky. "Weitere Studien ii. d. Entwicklung d. Ascidien." 

 Archiv f. micr. Anat., Vol. vn. 1871. 



(59) A. Kowalevsky. " Ueber Entwicklungsgeschichte d. Pyrosoma." Arch. 

 f. micr. Anal., Vol. XI. 1875. 



(60) Kupffer. " Stammverwandtschaft zwischen Ascidien u. Wirbelthieren." 

 Arch. 4 f. micr. Anat., Vol. VI. 1870. 



(61) Giard. " Etudes critiques des travaux, etc." Archives Zool. experiment., 

 Vol. I. 1872. 



(62) C. Semper. "Ueber die Entstehung, etc." Arbeit en a. d. zool.-zoot. 

 Institut Wiirzburg, Bd. n. 1875. 



Cephalockorda. 



(63) P. Langerhans. " Z. Anatomic d. Amphioxus lanceolatus," pp. 330 3. 

 Archiv f. mikr. Anat., Vol. xn. 1876. 



Craniata. 



(64) P.M. Balfour. "On the structure and development of the Vertebrate 

 Ovary." Quart. J. of Micr. Science, Vol. xvm. 1878. 



(65) Th. Eimer. " Untersuchungen ii. d. Eier d. Reptilien." Archiv f. mikr. 

 Anat., Vol. vm. 1872. 



(66) Pfliiger. Die Eierstocke d. Sdugethiere u. d. Menschen. Leipzig, 1863. 



(67) J. Foulis. "On the development of the ova and structure of the ovary in 

 Man and other Mammalia." Quart. J. of Micr. Science, Vol. xvi. 1876. 



(68) J. Foulis. "The development of the ova, etc." Journal of Anat. and 

 Phys., Vol. xin. 18789. 



(69) C. Gegenbaur. " Ueb. d. Bau u. d. Entwicklung d. Wirbelthiereier mil 

 partieller Dottertheilung." Mailer's Archiv, 1861. 



(70) Alex. Gotte. Entwicklungsgeschichte J. Unkc. Leipzig, 1875. 



(71) W. His. Untersuchungen iib. d. Ei u. d. Eientwicklung bei Knochenjischen. 

 Leipzig, 1873. 



(72) A. Kolliker. Entwicklungsgeschichte d. Menschen u. h'dherer Thiere. 

 Leipzig, 1878. 



(73) J. Miiller. " Ueber d. zahlreichen Porenkanale in d. Eikapsel d. Fische." 

 Mailer's Archiv, 1854. 



(74) W. H. Ransom. " On the impregnation of the ovum in the Stickleback." 

 Pro. X. Society, Vol. VII. 1854. 



(75) C. Semper. "Das Urogenitalsystem d. Plagiostomen, etc." Arbeiten a. 

 d. zool.-zoot. Instit. Wiirzburg, Vol. II. 1875. 



[Cf. Ludwig, No. 4, Ed. van Beneden, No. 1, Waldeyer, No. 6, &c.] 



