1880] A Review of the Modern Doctrine of Evolution. © 169 
row strips to complete roofs; in the fourth station on the line, 
these bones are rough, with a hyperostosis of their surfaces ; and 
in the next set of species, this ossification fills the skin, which is 
thus no longer separable from the cranial bones; in the sixth 
form the ossification is extended so as to roof in the temporal 
muscles and enclose the orbits behind, while in the rare seventh 
and last stage, the tympanum is also enclosed behind by bone. 
Now all of these types are not found in all of the families of the 
Anura, but the greater number of them are. Six principal fami- 
lies, four of which belong to the Arcifera, are named in the 
diagram below, and three or four others might have been added. I 
do not give the names of the genera which are defined as above 
described, referring to the explanation of the cuts for them, but 
indicate them by the numbers on the left margin of the page, 
which correspond to those of the definitions above given. A zero 
mark signifies the absence or non-discovery of a generic type. 
Sternum embryonic. Sternum complete. 
Bufoniformia. Arcifera, Raniformia. 
Bufonide. Scaphiopide Cystignathide. Hylide. Ranide, 
and Pelobatide. 
_ o o I I ò 
— 2 2 2 2 o 
-a 3 o 3 3 E 
s E; 4 4 4 4 4 
5— 5 5 o 5 5 
é— 6 6 6 6 o 
— 7 o o o o 
It is evident, from what has preceded, that a perfecting of the 
shoulder-girdle in any of the species of the Bufoniform and Ar- 
ciferous columns, would place it in the series of Raniformia, An — 
accession of teeth in a species of the division Bufoniformia, 
would make it one of the Arcifera; while a small amount of 
change in the ossification of the bones of the skull would transfer 
a species from one to another of the generic stations represented — 
by the numbers of the columns from one to seven. i 
There are few groups where this law of parallelism is so readi- 
ly observed among cotemporary types as the Batrachia, but it is 
_ Rone the less universal. The kind of parallelism usually observed 
= that in which there is only a partial resemblance between adults 
of certain animals and the young of others. This has been termed — 
_ VOL. XIv.—no, 111, 12 
