78 POPULAR SCIENCE MONTHLY. 



The young that develop from these comparatively large eggs inside 

 this peculiar skin-bag are remarkable enough to satisfy the ideals of 

 so bizarre a parent. Like the young Surxinam toad, these get their 

 front legs at a very early period, and at an early period are also found 

 without the adhesive organs and horny jaws that seem so essential to 

 all common tadpoles. But their chief departure from received tad- 

 pole style is the phenomenal character of the gills. These are large, 

 bell-shaped, flower-like membranes that envelop the tadpole like a 

 mantle and, coming between it and the walls of the mother's pouch, 

 may serve as a means of getting oxygen and possibly food from the 

 mother, for the gills are richly supplied with blood-vessels, and the 

 walls of the mother's pouch are also vascular, giving the anatomical 

 conditions for interchange such as takes place in a mammal's placenta. 

 Each of these two gills seems to have been made by the fusing of two 

 specialized gills, and each retains two stalks. Eventually these big 

 gills are probably lost and replaced by inside gills, just as in common 

 tadpoles the outside gills are always followed by inside gills. Whether 

 the mother goes into the water and lets the young escape where they 

 can use their gills, or whether she keeps them at home till they have 

 lost these youthful structures and can 'come out' in budding maturity, 

 is not known, in this case. But in Nonotrema marsupiatum and Noto- 

 trema plumheum the young are set free into the water when they are 

 still tadpoles. 



The way in which such a capacious pocket on the back can have 

 come about is perhaps indicated by the state of things in Nototrema 

 pygmcBum. The brood pouch is here small and slit-like, and when the 

 young are ready to leave it they press and wriggle till the pouch is torn 

 open, from the external opening forwards. There are only four to seven 

 young that can come forth in this partially Caesarian way, and their 

 appearance seems to have been prearranged by the way in which the 

 pouch is made. Two folds of the skin grow up to meet one another 

 along the back, and when they fuse they leave a sort of seam, which 

 is also the line along which the pouch ruptures to let the young out. 

 The pouch of this tree-frog is thus to some degree intermediate 

 between the simple cup on the back of Hyla Goeldii, not well shown in 

 Fig. 9, and the more perfect sac of the other pouched frogs described 

 above, and may indicate the lines along which structures and habits 

 like those of Hyla Goeldii could have been evolved in those of Noto- 

 trema oviferum. On the other hand, the small size of this frog and the 

 large size of its eggs make it both impossible to get the eggs into the 

 usual external opening of the pouch and impossible for the big larvae 

 to escape through it; hence it may be that the pouch grows up as 

 folds after the eggs are laid on the mother's back, and that these folds 

 remain easy of separation to allow the young to escape, all independent 



