1871.] 237 [Cope, 
is more or less departed from. In the Vertebrata the Amphiovus is 
almost completely bilaterally symmetrical. In the fishes, the digestive 
system is the only one which does not conform to it; while in the birds 
the reproductive system is atrophied on one side. In the serpents the 
respiratory and part of the circulatory are similarly modified; and in the 
mammialia the digestive and circulatory systems have both become un- 
symmetrical ; and the cranium even in the cetacea. 
If evolution be true, the unsymmetrical forms have descended from the 
symmetrical, and the asymmetry being thus not inherited, is the result 
of laws which have interfered with the original tendency to bilateral 
repetition. 
Many cases of bilaterally symmetrical diseases have been enumer- 
ated by physiologists, and I will select as an example one which has come 
under my observation. They were those of two boys who had had that 
disease involving the mucodermal system called Varicella, while the crowns 
of the successional incisor teeth were still enclosed in the mucous capsules 
of the alveolar walls. The deposit of phosphate of lime forming their 
surfaces was interrupted by the disease of the tissue, and the result was 
a surface pitted, or sculptured intaglio fashion. The sculpture of the 
two incisors of the right side was precisely imitated by those of the 
left in reversed order, even in minute details, which were numerous, thus 
producing a result not displeasing to the eye. This has been observed on 
two distinct occasions some years apart. 
Another interesting example of bilaterally symmetrical disease, is re- 
corded in a paper on ‘‘a case of universal hyperostosis, ete.,’”? by Drs. 
Mears, Keen, Allen and Pepper. * They describe the skeleton of a boy 
of fourteen which displayed an extraordinarly exostosed condition, the 
bones themselves remaining in the condition known as osteoporosis. 
They describe the uniform repetition of the abnormal growths of one 
side on the other in the following language, (p. 22). 
‘““Comparing the two sides externally, not only is there no difference 
in the extent and character of the disease, but there is the most remark- . 
able symmetry of the corresponding diseased bones, which may be traced 
even into details. The disease begins and ends on both sides at corres- 
ponding points, it changes in character from simple porosity to the 
growth of osteophytes at corresponding points ; if, on one side, the pos- 
terior part of the bone is most diseased, the same is true of the other 
side ; if the osteophyte growth is continuous or interrupted on one bone 
(fibula fig. 18), it is so on the opposite one ; if one is unusually diseased 
at a tendinous or aponeurotic insertion, so is its mate; if a groove ora 
variation in color exist on the one side, the same will be found on the 
other side ; even of single marked spicule of bone the same may be said, 
so that a description of one side will answer for both, minute differences 
being noted as they oceur.”’ 
6. Antero-posterior symmetry. 
That this is an absolute law of creation will be less readily admitted 
* See Proceed. Amer. Philos. Soc. 1870, p. 19. 
