THE EVIDENCE FROM DEVELOPMENT. 



239 



the long chains of eggs laid by the female round his thighs, so that he 

 seems to possess " trunk hose and puffed breeches," as Mr. St. Mivart 

 remarks. Dropping, in due course, into the water, the young burst 

 forth from the egg-coverings, and swim away, leaving their father-frog 

 once more unencumbered and free. 



Another frog (Rhinoderma Darwinii), a denizen of Chili, ex- 

 hibits another curious modification of a different kind. Rhinoderma, 

 like the edible frog of Europe, possesses certain " vocal sacs " or bags 

 placed within the mouth, whereby the resonance of the mouth and 

 the loudness of the croak are increased. 

 It is interesting to find, however, that 

 Rhinoderma has come to use its vocal 

 sacs as nests; the newly laid eggs 

 being thus received into the male 

 parent's pouches, and the young re- 

 maining therein till they attain a con- 

 siderable growth. We certainly know 

 of male fishes in the sea-horse genus 

 (Hippocampus) (Fig. 162), which carry 

 the young in a pouch ; and another 

 male fish (Arius fissus), like the Rhi- 

 noderma, carries the eggs in his 

 mouth and therein hatches them. In 

 Rhinoderma the vocal sacs are greatly 

 enlarged, and, in fact, extend on to 

 the flanks and belly of the animal. 

 From five to fifteen tadpoles were 

 found by Espada in each sac, the smallest being at the bottom. The 

 largest was about half-an-inch long, and had well- developed legs. 

 Neither the old nor the young tadpoles had any traces of gills, and 

 from their full development, the conclusion that the young are in 

 some way nourished in these sacs seems by no means far-fetched. 

 The Rhinoderma presents us, therefore, with a case in which the 

 organisation of the male has become curiously and permanently 

 altered to a decidedly new way of life so much so, indeed, that the 

 skeleton has become modified from the pressure of the curious egg- 

 sacs of the mouth. 



More curious still, on account of the very singular modification 

 which must have produced the feature in question, is the female 

 Pipa Americana or Surinam Toad, the skin of whose back becomes 

 soft at the breeding season. The eggs are pressed by the male into 

 this skin, which grows over them and encloses each in a kind of 

 cell. Very curious is it to find that in the cells of the maternal back, 

 not only the tadpole stage but the whole metamorphosis of this toad is 

 passed. The young toads develop a long tail within the egg, this 



FIG. 162. HIPPOCAMPUS, OR SEA-HORSE. 



