52 GENESIS OF MAN. 



during life, as do the Dipneusta, undergo a complete metamor- 

 phosis after birth, passing from a true fish-form, in the tadpole 

 state (in which, in addition to the well-known external fish-like 

 characters, they also possess gills and no lungs and a correspond- 

 ing piscine circulation) to the familiar batrachian form, in which 

 their respiration is through lungs only and their circulation through 

 two auricles. Now, the two sub-classes above named furnish the 

 most perfect and characteristic transition stages between the larval 

 and adult stages of the higher amphibians. The Sozobranchia, as 

 the term implies, preserve their gills through life, but also acquire 

 lungs, and are therefore strictly amphibious. They live, however, 

 chiefly in the water, and there perform all the functions of their 

 existence. The greatest excitement in scientific circles has been 

 recently called forth by the extraordinary conduct of a member of 

 this group. The Mexican Axolotl (Siredon pisciformc) was observed 

 in the Paris Jardin des Plantes, where large numbers of these 

 creatures were kept, to frequently take to the land, and several 

 individuals so far habituated themselves to terrestial life that they 

 actually lost their gills in the manner of the higher amphibians. 

 Individuals thus behaving were scarcely distinguishable from the 

 Ambly stoma, a genus of the Sozura which acquire lungs. 



An equally remarkable phenomenon, but of exactly the opposite 

 class, was manifested by the Triton, which belongs to the last 

 named sub-class, and therefore habitually undergoes the metamor- 

 phosis common to frogs, etc., only without the loss of the tail. 

 Before it arrives at maturity, the Triton, under ordinary circum- 

 stances, loses its gills and leads a sub-terrestrial life, breathing 

 only air. But by placing it in a tank so shaped that it was unable 

 to get out of the water, it was thus compelled to retain its gills 

 through life, and even propagated in the water. 



All animals above the amphibians are characterized by the pos- 

 session, during their embryonic stages, of the important organ called 

 the amnion, which is wanting in all below them, and in the amphib- 

 ians themselves. The facts of ontogenesis, as well as those of com- 

 parative anatomy, justify the assumption of the former existence, 

 probably in the beginning of the Mesozoic age, of a lizard-like 

 animal whose fossil remains have not yet been discovered, and 

 whose affinities with any known living form are not close, but 

 which must have been the first to develop this particular organ, 



