NOTES ON BATRAOHIANS OF THE PARAGUAYAN CHACO. 325 



Again, we find this difference in general development of 

 the young larva intensified in such forms as undergo a 

 still more abbreviated embryonic development ; for instance, 

 in Paludicola fuscomaculata, where the embryonic de- 

 velopment is shortened to something between twelve and 

 twenty-four hours. All the points in which E.ana appears 

 to be a more modified form of development than Phyllo- 

 medusa are intensified, and the external characters are ill- 

 defined. However, a minute comparison cannot yet be tnade 

 until I shall have had time to study more carefully the details 

 of development in Paludicola. The study of the internal 

 anatomy leads to the same conclusion, namely, that in this 

 protracted development we do not find the course of develop- 

 ment distorted and blurred, but on the contrary every organ, 

 so far as I can find, develops as in the ordinary frog, only 

 more clearly and more definitely, and at the same time more 

 as we see it develop in other great groups, Elasmobranchs, 

 Ganoids, and the higher Vertebrates. 



Take for instance the eye of a free-swimming batrachian 

 larva, and compare it with the eye of Phyllomedusa. The 

 evolution of the optic cup and lens is hurried over and 

 blurred in the former, so that they are often difficult to trace, 

 while here in Phyllomedusa it is as regular and diagrammatic 

 as in any Vertebrate there is. Contrary to what we find in 

 most Batrachia, the lens develops as an involution of a single 

 layer of nervous epiblast rather than a mere thickening of that 

 layer. In the free-swimming form the eye has been required to 

 become functional as rapidly as possible, while here it has been 

 suffered to go through its normal course of development in peace. 



Take again the suckers of the free-swimming forms. 

 They are evidently new adaptations without phylogenetic sig- 

 nificance. Through the presence of these structures the form 

 of the mandibular arches has become quite obliterated, while 

 here in Phyllomedusa these would compare favourably with 

 those of an Elasmobranch, reptile, or bird. 



The peculiarly symmetrical gastrulation that this egg 

 exhibits must be supposed, I think, to be the effect of a large 



VOL. 42, PART 3. NEW SERIES. Y 



