68 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



That the above generic divisions have been actually 

 developed from each other is demonstrated by the oc- 

 currence of occasional intermediate forms. Thus no 

 generic distinction can be maintained between types 

 third and fourth in the family of toads (Bufonidae), so 

 complete is the transition between them. In Hylidae 

 and Cystignathidae occasional transitions between types 

 second and third occur. In the Scaphiopidae the sub- 

 species Spea hammondii intermontana sometimes has the 

 frontoparietal fontanelle open, sometimes closed. I 

 have seen some adult specimens of Rana virescens au- 

 stricola from Central America with the ethmoid bone 

 unossified above, as in the genus Ranula. The rugose 

 cranium is only acquired in old age of some of the spe- 

 cies of Polypedates of India. Yet these genera are as 



EXPLANATION OF CUTS OF CRANIA OF SALIENTIA. 



The numbers in each column correspond with the types of ossification 

 mentioned in the text, and are the same as those in the table of families given 

 in the same connection. The power numbers attached to No. 4, represent the 

 degree of ossification of the nasal bone, except -l, which signifies unossified 

 ethmoid. Most of the cuts are original. 



Fig. 18. BUFONIDAE. No. i, anterior part of skull of Chelydobatrachus 

 gouldii Gray, from Australia. No. 4, do. of Schismaderma carens Smith, South 

 Africa. No. 5, 'top of head of Peltaphryne peltacephala D. and B., Cuba. No. 

 7, top of head of Otaspis empusa Cope, Cuba. 



Fig. 19. SCAPHIOPID.E AND PELOBATiD^E. No. 2, diagram of top of cranium 

 of Didocus calcaratus Micahelles, Spain. No. 5, skull of Scaphiopus holbrookii 

 Harl., United States. No. 6, skull of Cultripes provincialis, from France, after 

 Duges. 



Fig. 20. HYLID-E. No. I, Thoropa miliaris Spix., Brazil. No. 2, Hypsi- 

 boas doumercii D. and B., Surinam. No. al, Hypsiboas punctatus Schn., Brazil. 

 No. 4^, Scytopis venulosus Daudin, Brazil. No. 5, Osteocephalus planiceps Cope, 

 E. Peru. No. 6, Trachycephalus geographicus D. and B., after Steindachner. 



Fig. 21. CYSTIGNATHID.*. No. i, Eusophus nebulosus Gir., Chili. No. 2, 

 Borborocoetes tasmaniensis Gthr., Tasmania. No. 3, Elosia nasus Licht., Bra- 

 zil. No. 4, Hylodes oxyrhynchus D. and B., West Indies. No. 6, Calyptocepha- 

 lus gayi D. and B., Chili. 



Fig. 22. RANID.E. No. 4- 1, Ranula ckrysoprasina Cope, Costa Rica. No. 

 4!, Rana clamata Daud., N. America. No. 48, Rana agilis Thomas, Europe. 

 No. 48, Rana hexadactyla Less., India. No. 5, Polypedates quadrilineatus D. 

 and B., Ceylon. 



