NOTES ON BATRACHUNS OF THE PARAGUAYAN OHACO. 321 



consist in the appearance of the second pair of external gills, 

 which do not reach nearly so high a state of development as 

 the first pair ; also in the rapid growth of the first pair of gills, 

 so as to extend beyond the vent as blood-red filaments through 

 which the corpuscles stream along, propelled by the now rapidly 

 pulsating heart (figs. 25, 27, 17 — 19). 



A dense plexus of vitelline veins ramifies over the surface of 

 the yolk, while the dorsal aorta and cutaneous veins give to the 

 elongated tail a copious supply of blood (fig. 29). Indeed, so 

 noticeable is this, that I am quite inclined to agree with Mr. 

 Kerr's suggestion that the tail of this larva is an important 

 organ of respiration. This view is further strengthened by 

 my observation that in hatched larvse the tail often remains 

 motionless as a whole, while the extremity of the tail is 

 kept rapidly vibrating. As the larvae are not propelled 

 by this motion through the water, I am tempted to think 

 that the object of it is that a stream of water may be 

 kept constantly running along the surface of the proximal 

 part of the tail. 



The operculum now grows down from the hyoid arch and 

 encloses the gill arches. The external gills become rapidly 

 absorbed (but I think that a study of the origin of the fila- 

 ments of the internal gills shows them to be really of the same 

 nature as the external gills), the stomatodaeal aperture breaks 

 through, and the young frog has reached the end of its em- 

 bryonic life (fig. 26). 



Internal Characters. — On account of the short space of 

 time at my disposal it seems advisable not to attempt a con- 

 tinuous account of the internal phenomena of development, 

 but merely to figure and describe sections illustrating some of 

 the more important points of interest, leaving the fuller 

 account for a future occasion. 



Section I^ passes transversely through the blastopore before 

 the formation of the neural groove. The main points to be 

 noted are the smallness of the archenteron, the absence of a 



' The numbers bere given correspond with those of the figures of Plates 

 31 and 32. 



