NOTES ON BATRACHIANS OP THE PARAGUAYAN OHACO. 319 



The neural folds now begin to approach one another at the 

 anterior and posterior ends of the groove, but there is no well- 

 marked anterior transverse fold (fig. 12). 



Posteriorly the folds enclose the remains of the blastopore, 

 which then opens only into the neural canal formed by the 

 complete fusion of the edges of the two folds. A tail fold 

 develops of a crescentic form encircling the posterior end of 

 the neural plate, on the posterior convex side of which the 

 anus is formed (Section III, an.). 



Between the blastoderm and the egg membrane there is now 

 present a considerable space, filled with a milky fluid (fig. 

 12, sp.). 



When the neural folds have completely met, i. e. fifty hours 

 after laying, then the anterior end of the neural plate expands 

 to form the optic vesicles, and an elevation extends forwards 

 from them, homologous with the so-called '^ Sense -plate " of 

 Morgan. Behind the optic vesicles extending laterally and 

 anteriorly on either side is seen the gill-plate or branchial fold. 



Later this grows to completely encircle the sense-plate, which 

 now shows a depression at the anterior end, the rudiment of 

 the stomodEeum (fig. 20, Stom.). 



The right and left halves of the '' sense-plate ^' thus divided 

 are very conspicuous features at this stage in development, and 

 for some time later. A little later they become formed into a 

 regular pair of mandibular bars, which only just meet below 

 the stomodseum (fig. 21, Mnd.). 



In section they appear quite like the succeeding hyoid 

 arches, which are very slightly developed, and also the larger 

 first and second pair of branchial arches. 



There is a total absence of suckers such as are borne behind 

 the mouth in most Batrachian larvse, and the embryo has now 

 more the appearance of a young larva of Acipenser than of 

 Ran a. 



The gill-plate in life appears as a single elevation on either 

 side, but after fixing with appropriate reagents it may be seen 

 almost from the first to consist of three branchial pouches of 

 the pharynx ; the two anterior of these alone persist. The 



