cavity. During the passage through the oviduct, the ovum is 

 covered by gelatinous material secreted by the walls of the 

 oviduct, which Baer equated to the albumen of a hen's egg. 



Fertilization in the tailless amphibia is external; 

 the sperm cover the ova falling into water. In salamanders 

 the sperms also are ejected into water before they penetrate 

 the genital apparatus of the female. 



The structure of the deposited ova and the early stages 

 of development Baer described in Miiller's ARCHIV in 1834 

 and below. 9 The freshly deposited ova closely adjoin each 

 other and are covered by compact albumen. In water the 

 latter is swollen and becomes transparent. Meanwhile the 

 ovum becomes spherical and begins to turn in its membrane, 

 directing the dark side upwards. Baer called the upper and 

 lower regions of the frog ovum the dark and light surfaces; 

 their centers he called the dark and light poles and the 

 line joining the poles the axis of the ovum. 



Concerning the first stages of development of the 

 fertilized frog ovum, Prevost and DumaslO reported their 

 observations. According to them, "astonishing division" 

 takes place on the surface of ovum as Baer had said. These 

 observations, Baer reported, "caused a lively interest in 

 all directions, partly due to the unexpectedness of the 

 fact that the yolk sphere, which will become a frog, is 

 preliminarily covered by a network of geometrically and 

 regularly situated fissures. It was due, also, to the 

 apparent improbability that such a noticeable phenomenon had 

 escaped the attention of many observers of the development 

 of ^the frog ovum, including Swammerdam" (106) . Although 

 Prevost and Dumas did not understand the essence of the 

 division phenomenon, Baer accurately stated that they 

 "remained on the surface of the phenomenon" (MULLER'S 

 ARCHIV, 1834, pp. 482-483). Rusconi 11 also saw the same 



9. Baer, "Die Metamorphose des Eies der Batrachier vor der 

 Erscheinung des Embryo und Folgerungen aus ihr fur die 

 Theorie der Erzeugung." 



10. J. L. Prevost et J. A. Dumas, "Nouvelle theorie de la 

 generation," ANN.^SC. NATUR. , 2 (1824), pp. 100-121, 129-149 



11. M(auro) Rusconi, DEVELOPPEMENT DE LA GRENOUILLE COMMUNE 

 DEPUIS LE M3MENT DE SA NAISSANCE JUSQUE A SON ETAT PARFAIT 

 (Milan: Giusti, 1826) . 



420 



