240 CHAPTERS ON EVOLUTION. 



appendage being absorbed before they are hatched, whilst the useless 

 gills disappear at a very early period in larval existence. Over 120 

 cells have been counted in the back of this toad, and from these cells 

 the young emerge as miniature facsimiles of the parent Another 

 noteworthy case of altered development is that of the Hylodes Martin- 

 icensis, which passes through the whole of its metamorphosis within 

 the egg, and emerges, as do the young of the Surinam toad, a perfect 

 frog, which otherwise would require to pass several weeks in water 

 to complete its development. 



Now, to what conclusions do such facts lead us respecting the 

 modification and alteration of development? It is perfectly clear that, 

 as frogs and toads are normal tenants of the water in their early and 

 tadpole stages, and are provided with gills as aquatic forms, those 

 species which pass the whole of their development in the back of the 

 mother, or even within the egg, must represent the most modified 

 members of the frog class. We are therefore entitled to take their 

 case as illustrating the best marked of the tendencies to alteration 

 which the race presents. A frog which, like Alytes, carries the eggs, 

 but drops them into water when they are ready to leave their primary 

 abode, represents the first stage of modification. We are led a 

 little farther on the way towards a suppression of metamorphosis 

 by the case of the Hylodes, which lays its eggs in the axils of leaves, 

 where moisture is relatively scarce, but where development is never- 

 theless undergone in due course. More advanced is the Surinam 

 Toad, where the young pass their entire metamorphosis within the 

 egg and in the mother's back ; the Hylodes Martinicensis being but a 

 further development still, seeing that in this frog the whole develop- 

 ment is carried on within the egg, and metamorphosis is therefore 

 practically hidden and unseen. 



We may not doubt, therefore, that the amphibian class ex- 

 hibits thus a tendency towards direct development or that without 

 metamorphosis. Imagjne the result of the later stages of such a 

 modification of reproductive habits and customs. Hylodes Martin- 

 icensis, for instance, is now practically in the position of an 

 animal which undergoes all its changes within the egg, and which, 

 in all probability, will, in time, further shorten and condense its 

 life-history. If such changes and modifications are occurring before 

 our eyes to-day, is it unreasonable to regard all ordinary and 

 direct developments and amongst others, those of fish, reptile, 

 bird and man as in reality abbreviated and "brief chronicles" 

 of once extended chapters in animal histories ? A fish or bird 

 passing through its development within the egg undergoes a meta- 

 morphosis it is true, but shortened and condensed as compared with 

 that of the frog. There is no reason against the supposition, but 

 every circumstance of life favouring it, that once upon a time fish- 



