THE FROG AS PARENT. 79 



of any mode of development of the pouches of other marsupial frogs. 

 These strange skin pits and bags of the Surrinam toads and the Ven- 

 ezuelan 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 know- 

 ing 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 



