238 (Dee. 15. 
Cope. ] 
than in the case of double bilateral symmetry, since the exceptions appear 
to be so universal. Nevertheless, I believe it to be as much a part of the 
law of Repetitive nutrition as the other. The antero-posterior homolo- 
gies even of the human skeleton have been largely demonstrated, but as 
usual, we must appeal to the lower forms for a clear view of it. In the 
rudimental skeletal axis we find such symmetry almost perfect in the 
Amphiorus, but in no other vertebrate. In limbs we have it clearly in- 
dicated in the Reptilian order Ichthyopterygia, and in the Piscine order 
Dipnoi, where the anterior and posterior are scarcely or not all distin- 
guishable. In the scapular and pelvic arches we find it also approximated 
in the first-named orders. 
In the nervous system it also exists approximately in the Amphiozus. 
It is not seen in any vertebrate, and in but few other animals, in the di- 
gestive system, but it appears to exist in some lower articulata in both 
the respiratory and circulatory s ystems. 
c. As illustrations of exact repetition involving large portions of the 
organism the higher Polyps may be cited, which differ from the lower 
chiefly by the addition of similar septa and similar tentacles. Examples 
of repetition of nearly the whole organism, may be found in many Entozoa 
as Taenia, where the cephalic segment only differs from the others, the 
remainder or proglottides being alike. ‘The most entire repetition of 
structure is seen in Vibrio, where the segments are all alike, there being 
none representing a head. 
d. Asan example in special details of structure, the segments of the low- 
est brain (that of the lamprey) are repetitions of the first one. The 
pelvic arch of Ichthyosaurus when first created, was a repetition of 
the scapular, and the hind limb, of the fore limb. The segments of 
the limbs of the Dipnot are mere repetitions, the later created of the 
earlier. The special parts of the pes and manus of Ichthyosaurus are 
simply repetitive efforts of growth-force joined with a diminishing 
amount. The addition of a digit often distinguishing one genus of Sala- 
manders or Saurians from another, is evidence of a similar repetitive 
effort. The low mammal Ornithorhynchus, possesses but a single tooth 
in each jaw ; the simple teeth of armadillos and cetaceans, increasing as 
they have done from a single commencement as in the monotreme cited, 
present examples of repetitive acceleration of growth force. 
e. Complication of a single element of repetition is accomplished appar- 
ently by a double repetition. This is best understood by the consider- 
ation of the transition from simple to complex teeth. In the cetaceans 
this occurs in the Squalodonts ; the cylindric incisors are followed by 
flattened ones, then by others grooved on the fang, and then by two 
rooted, but never double-crowned teeth. This is the result of antero- 
posterior repetitive acceleration of the simple cylindric dental type of the 
ordinary toothed cetacean. 
