234 [Dee. 15, 
Cope. ] 
parallelisms’’ should be exhibited in a reversed order. Parallelisms, it is 
true, are exhibited; but so far as I have observed always ‘“‘inexact,’? 
often in a high degree. A marked case of retardation occurs in the den- 
tal development of a number of persons who have come under my obser- 
vation in the neighborhood of Philadelphia. It is not very uncommon to 
find persons in whom the third molars in both jaws are incomplete as to 
number, one, two, three, or all, being deficient. It is still more common 
for them to be incompletely covered by the enamel layer, and to become 
in consequence so worthless as to require early removal. Jam acquainted 
with two families in which the absence of the exterior upper incisor on 
each side is common. In one of these the second and third generation 
have inherited it from the mother’s side, and it now characterizes many 
of the children. The significance of this modification will be best under- 
stood by examining the dental structures of the Quadrwmana in general. 
Jommencing with the highest family and its abnormal dentition, we 
have :— 
Incisors. Canines. Premolars. Molars- 
2 2 
Dy 
¢ Abnormal. 
1 1 
Hominnd es { Normal. 2 5 
ISUNMO: suis es ea eye Z i é 
CONE AT ee ones $ ‘ 3 
DEMUridt es (ert a ; 2 : ee 4 
Mammalia, Normal...... 8 : 5 
In this table we see a decline in the number of teeth of the higher 
groups. Thus, the premolars are one less than the normal number in the 
whole order, and they lose one in each jaw in the Old World apes, and 
man. The molars maintain the normal number throughout, but the third 
in both jaws is in the Simiide reduced by the loss of a fifth or odd tuber- 
cle,thus becoming four-lobed. In the upper jaw, this is first lost in 
the Semnopithecus; in the lower, in the next highest genus Cercopithecus. 
In Homo its appearance is ‘‘retarded,’’ the interval between that event 
and the protrusion of the second molar—six to ten years-—being relatively 
greater than in any genus of Quadrumana. Its absence is then the re- 
sult of continued retardation, not of a new and adaptive suppression, and 
is of direct systematic zoological value. 
In the incisors a reduction. is also plainly visible, as we pass from the 
most completely furnished mammals to the genus Homo. One from the 
upper jaw is first lost, then in the Cebida, one from the lower also. The 
number remains the same through the Stmiide and normal Hominida, 
but in the abnormal cases cited, the process of reduction is continued and 
another incisor from each side disappears. That this also is truly ‘‘re- 
tardation”’ is also evident from the fact, that the exterior incisor is the 
last developed, being delayed in ordinary growth a year later than those 
of the inner pair. The same retardation is seen in the quadrumane Cheir- 
omys (the Aye-aye), and the whole order Rodentia. In the latter, the 
rare presence of the reduced second incisors, as in Lepus, shows a less de- 
