796 
232 [Dec. 15, 
Cope. } 
never found to vary, but which differ in the same point as those in which 
I have observed the above variations, are also derived from common par- 
ents, and the more advanced have been accelerated or the less advanced 
retarded, as the case may have been with regard to the parents. 
This is not an imaginary case, but a true representation of many which 
have come under observation. The developmental resemblances men- 
tioned are universal in the animal, and probably in the vegetable king- 
doms, approaching the exactitude above depicted in proportion to the 
near structural similarity of the species considered. 
Heample 1. It is well knownthat the Cerside of the Old World develop 
a basal snag of the antler, (see Cuvier, Ossemens Fossiles, and Gray, Cat. 
British Museum,) at the third year; a majority of those of the New 
World (genera Subulo, Cariacus) never develop it’ except in abnormal 
cases in the most vigorous maturity of the most northern Cariacus (0. 
virginianus), while the South American Subulo retains to adult age the 
simple horn or spike of the second year of all Vervida. : 
Among the higher Cervida, Rusa and Axis never assume characters 
beyond an equivalent of the fourth year of Cervus. In Dama the char- 
acters are, on the other hand, assumed more rapidly than in Cervus, its 
third year corresponding to the fourth of the latter, and the development 
in after years of a broad plate of bone, with points being substituted for 
the addition of the corresponding snags, thus commencing another series 
which terminates in the great fossil elk, Megacerus. 
Returning to the American deer we have Blastocerus, whose antlers 
are identical with the fourth year of Cariacus. Corresponding with the 
Dama-Megacerus type of the Old World we have the moose (Alces) de- 
veloping the same palmate horn en the basis of Cariacus (¢. ¢., without 
eye-snag. ) 
Example 2.—I select the following series, embracing the majority of 
the genera of the North American Helicide.* 
1. Turns of spire very few; wide umbilicus; shell thin, with thin 
... Binneya. 
2. Turns few, but more; 1 Vitrina. 
3. Turns still more numerous; rest as above.. digrs  eddy eas 
4, As No. 8, but lip thickened.inside..'..:4...-.. Ce ea ce Hlygromia. 
5. Coiled; umbilicus closed, lip thickened inside and out, 
Tachea and Pematia. 
6, Same, with a parietal COO... «4.6, ees eee cys Cieeect Mesodon. 
7. Same, with parietal and two interior lip teeth.......Zsognomostoma. 
* * Recommencing at No. 4. All with open wmbilicus. 
5. As No. 4, but lip thickened in and out. . .. Artonta. 
6. Same as No. 5, but with parietal tooth. See rere eh OU NVC 
7, Same, with both parietal and lip teeth........... : rtodopsts. 
* See Tryon, Terrestrial Mollusca of the United States. Probably other (e.g. dental) 
characters distinguish some of these genera, but the above furnishes the history of one 
set of characters. 
