eS PIEN a ee ee ee ae 
: bore 
* 
1885.] Progressive and Retrogressive, 245 
retrogression may be answered as follows: If degeneracy con- 
sists in “the loss of parts without complementary addition of 
other parts,” then the Batrachian line is a degenerate line. This 
is only partly true of the vertebral column, which presents the 
most primitive characters in the early, Permian, genera (Rhachi- 
tomi). If departure from the nearest approximation to the Mam- 
malia is degeneracy, then the changes in this class come under 
that head. The carpus, tarsus and scapular and pelvic arches of 
the Rachitomi are more mammalian than are those of any of their 
successors, : 
There are several groups which, show especial marks of degen- 
eracy. Such are the reduced maxillary bones and persistent gills 
of the Proteida; the absence of the maxillary bones and the 
presence of gills in the Trachystomata; the loss of a pair of 
legs and feebleness of the remaining pair in the sirens; and the 
extreme reduction of the limbs in Amphiuma. Such I must also — 
regard, with Lankester, the persistent branchiz of the Siredons. 
I may add that in the brain of the Proteid Necturus the hemi- 
spheres are relatively larger than in the Anura, which are at the 
end of the line. 
It must be concluded, then, that in many respects, the Batrachia 
have undergone degeneracy with the passage of time. 
VI. Tue REPTILIAN LINE. 
As in the case of the Batrachia, the easiest way of obtaining a 
general view of the history of this class is by throwing their 
principal structural characters into a tabular form. As in the 
case of that class I commence with the oldest forms and end with 
the latest in the order of time, which, as usual, corresponds with 
the order of structure. I except from this the first order, the 
Ichthyopterygia, which we do not know prior to the Triassic 
period 2 
A. Extremities not differentiated in form beyond proximal segment. 
I. Os quadratum immovably articulated to squamosal, etc. 
Tubercular and capitular rib articulations present and distinct. ..1. Jchthyopterygia. - 
AA. Elements of extremities differentiated. 
. | Generally similar to the system published by me. Proceedings Amer. Ass. Adv. 
Science, xix, p. 233. 
