DEVELOPMENT OP THE SKULL IN THE BATRACHfA. 3 



But the ideal Prot.ohatrachians came up by the way of the Sucking Fislies (" Marsipo- 

 brauchii "), and grazing the edge of the Chimreroids and ordinary Sehxchians, developed 

 into the larval form (or Tadpole) _/{?'S^ I am under the impression that in many oases 

 the tailed gill-bearing condition has only lately been completely departed from, and 

 that the anurous form or stage of such a type as Pseudis has only become universal 

 in the newer geological times. 



Whilst these tailed forms — hy[)otheticolly the primary condition of the Batrachia 

 — have been yielding to terrestrial influences, and undergoing more and more cur- 

 tailment and general metamorphosis, they have also, from time to time, dropped 

 out of their organisation much of their old bony armour ; and tliat which has been 

 retamed has become less and less superficial (or " dermosteal "). 



They have to a remarkable degree lost their mandibular, and in many cases their 

 maxillary teeth also ; tliis has been evidently a correlate of the development over 

 the ventral end of the hyoid arch of a peculiar cushioned fold of the floor of the 

 mouth — the tongue. As this fold has become a more and more effective prehensile 

 organ, the teeth have become less and less useful to the creature, whose succulent 

 " articulate " or " molluscous " food is caught suddenly, and swallowed whole. 



The size of these types has evidently undergone a steady secular diminution ; this, 

 and in many cases an exquisite specialisation of the fingers and toes, has all been in 

 their favour ; up high in the trees of the forest, and variously painted to resemble their 

 surroundings of bark, leaves, and flowers, these marvels are wrought in them by the 

 " Archchemic Sun ;" — their small size, I say, their curiously mimicking coat, and their 

 high nestling, give them a chance of life and of life's enjoyments equal to that given 

 to any tribe of animals whatever. 



As in the common living forms now, the dilemma for the larval Batrachian is to 

 "transform or perish" in short annual periods; so, I opine, in long-past secular 

 periods, again and again, those tribes — the forefathers of our existing kinds — have 

 been put to the same extremity of shifting for their lives. 



As the earth was made to be inhabited, and as the evolution of its tribes takes 

 place throvigh the harmonious inter-action of the forces within the organisms and the 

 influences surrounding them, it has come to jiass again and again that the extremity 

 of some archaic form has been Nature's opportunity; its threatened extinction has 

 been the occasion of its transformation into a higlier kind of being, and the drying up 

 of the old waters has been followed by the peopling of the new land with fresh and 

 fresh forms, enjoying in many ways " newness of life." 



There are two main groups of dwarf forms, namely, the highly developed and 

 typical Tree-frogs, and the arrested, low kinds, such as the " Engystomidaj " and 

 "Phryniscida3 ;" these latter appear to be waifs and strays from old and extensive 

 tribes that have gone down in the world and are becoming gradually extinct; the 

 " Hylidse " (like the smallest " Carinate " birds), being Frogs of high degree, are in 

 no such danger of extinction. 



B 2 



