Page:Popular Science Monthly Volume 59.djvu/89

Rh of any mode of development of the pouches of other marsupial frogs. These strange skin pits and bags of the Surrinam toads and the Venezuelan frogs are both an aid to the young and an inconvenience to the parent, and it seems in keeping with our general experience that it is the female that has these special organs and the female that suffers the dangers that go with the prolonged care of the offspring. In both respects, however, with regard both to the phenomenal nature of the breeding organs and in the amount of personal sacrifice, this female is outdone by the male of a little frog of Chili.

This frog is not much more than an inch long, and was first found by Darwin on the voyage of the 'Beagle.' In some unknown way the large eggs get into the mouth of the male and are carried a long time inside a huge sac that opens only into the front part of the mouth. In this pouch the young develop their legs and small tails. It is probable that they remain protected within the male till they are complete lung-breathing frogs and then get out of his mouth and escape. Why he does not eat them is a question that might naturally occur to one knowing only our common frogs.

The brood-sac of this male extends over the throat and belly, back to the loins and up on each side nearly to the backbone. The eggs and young that are found in it are from five to fifteen in number, and lie scattered about in the capacious chamber. The general anatomical relations of this sac are shown in the rude diagram. Fig. 12. This represents some of the organs that would be seen on cutting the frog into halves, lengthwise. The brain and spinal cord along the back are shown in black. Below this are the mouth, stomach and intestines. On the floor of the mouth is an elevated region, the tongue; behind this is the opening to an irregular cavity, one of the lungs. In front of the tongue is the opening to a very large sac, the brood-sac, in which the eggs are represented as large balls.

A bag of this size necessarily causes the skin of the throat to bulge out and also presses upon the internal organs. It is found that even the bones of the shoulder girdle and chest are modified in connection with this remarkable organ, and that the stomach, liver and intestines may be pressed out of place, so that feeding must be difficult. In some cases the digestive organs are said to be so impaired as to be of no use, while in other cases the brood-sac is of much less extent and would seem not to interfere seriously with feeding and digestion.

The brood-sac lies free under the skin, except in certain regions of the throat, where it is fastened to the skin. The lining of this sac is a continuation of the lining of the mouth, in fact, the sac is but an enormous side pouch from the mouth. In looking for any similar organ in common frogs, we find the single or paired resonance chambers that open into the mouth and serve to give volume to the voice. These