embryo, so that for the following stage of life nothing remains 

 excessive, contrary to mammals, birds and reptiles. 16 There- 

 fore the entire rudiment must be considered as the embryo" 

 (II 11 f; p. 380 (286)) . 



At the time of closure of the back, the embryo changes 

 from a spherical to an elongated form. In the anterior part of 

 the trunk, in the region of abdominal layers of both sides, 

 the branchial protuberances appear stretched downwards; there 

 the parallel fissures form. Towards them from the inside, 

 deeper fissures grow, and the branchial slits originate in 

 this way. Earlier observers saw only three branchial slits, 

 but in his monograph published in Bardach's "Physiology," 

 Baer proved the existence of four slits. 17 Rusconi saw 

 the same, and also found a questionable fifth slit. The 

 surface of the branchial arches has nodules, which are trans- 

 formed into delicate branched protuberances supplied by blood 

 vessels and then transformed into external gills on three 

 branchial arches. 



The development of brain and organs of sensation takes 

 place as in higher vertebrates, only the bends are less 

 pronounced. 



When the tail reaches the length of the trunk and the 

 external gills are already well branched, the embryo ruptures 

 the yolk and gelatinous membranes. Hatching occurs at a very 

 early stage of development in comparison with birds. 



The larvae coming out from the membrane are attached to 

 the jelly covering the spawn, or to other objects in the 

 water by special suckers, which disappear shortly afterwards. 

 Initially, the larvae eat the jelly and frequently the dead 

 bodies collected by it, and with the appearance of extremities 

 they move to plant food. At this time the internal gills are 

 formed, and the opercular fold covering them grows with an 

 orifice to the outside. 



16. In Baer it stands — "amphibia." This is either a misprint 

 or an application of Linneaus* designation of a group which 

 includes amphibia and reptiles. 



17. (Ed.: Karl Friedrich Burdach, DIE PHYSIOLOGIE ALS 

 ERFAHRUNGSWISSENSCHAFT, Bd. I (1826), Bd. II (1828).) 



429 



