62 INVERTEBBATE MOBPHOLOGT. 



" winter eggs " which develop after fertilization. Here no 

 difference of form exists between the two generations, but 

 such cases, as well as those in which two sexual generations 

 unlike in form and habitat alternate with each other, are 

 usually associated with the more typical examples as in- 

 stances of heterogony. 



LITERATURE. 



0. Hertwig. Beitrage zur Kenntniss der Bildung, BefrucMung und TheUung 



des thierischen Mes. Morpholog. Jalirbucli, i. , iii. and rv. 1875-78. 

 E. van Beneden and A. Neyt. Nouvelles recherches sur la fecandation et la 



dimsion mitosique chez I'Ascaride megalocephale. Bulletin de la Societe 



royale Belglque, xiv. 1887. 

 Th. Boveri. Zellenstudien. Jenaische Zeitsclirift, xxii. 1888 and xxiT. 1890. 

 H. Fol. Le quadrille des centres. Archives des Sciences phjs. et naturelles 



Genfeve, xxv. 1891. 

 0. Hertwig. Vergleich der M- und Samenbildung bei Nematoden. ArcMv 



fill- mikrosk. Anatomie, xxxvi. 1890. 

 r. M. Balfour. A Treatise on Cmnparatim Embryology. London, 1880. 

 E. Jletsclinikoff Embryologische Studien an Medusen. Vienna, 1886. 

 E. Haeckel. Die Gastrula und die Eifurchung der Thiere. Jenaische Zeit- 



schr., IX. 1875. 



