LAW OF ACCELEKATION. 41 



compressed, involute forms like Schloi. Charmassei, the suppression, so far as we 

 know, always occurred in normal forms at some nealogic stage, and the presence 

 of a channel is constant even in the young. If the pilse again crossed the 

 abdomen, thus obliterating or obscuring the channel, during the life of the 

 same individual, it occurred as a degradational character in the senile stages. 

 Extreme cases of degradation in species did not occur in Schlotheimia, but if 

 there had been any such nostologic forms, they would have inherited this ten- 

 dency to obliterate the channel during the nealogic stages. The law of ac- 

 celeration of development was quite as effective in its action upon geratologous 

 as upon progressive characters, as will be seen when we treat of this class of 

 characters farther on. 



Besides the examples given above of the inheritance of characters in larger 

 and smaller series, we add the following in order to make our meaning still clearer. 

 The form, shape, and characteristics of the secondary radical, Psil. planorbe, are 

 prominently shown in the young of Arnioceras, Plate II. Fig. 10-15, and in the 

 Embryology of Cephalopods, Plate II. Fig. 9, 10, until a late period of the 

 growth of the shell, but are less noticeable in the young of the descendent 

 species, Cor. kridion, in which indeed they are perceptible only in the transition 

 form between this species and semicostatum. Most of the specimens have young 

 like that figured on Plate III. Fig. 2, and are stouter than the flat discoidal Psil. 

 planorbe. These and the young of other species of Coroniceras inherit the stouter 

 quadragonal whorl and peculiar ribs and tubercles, the keel, and the channels, 

 at earlier stages of their growth than those in which they first appeared in ances- 

 tral shells, as may be seen by comparing Am. semicostatum with the young of 

 Coroniceras, Plate III. Fig. 19, and Fig. 5, 6, 8-10. 



One of the most convincing examples of the law of acceleration which we 

 have studied can be illustrated by using Wright's book, " Lias Ammonites." 1 He 

 shows the latsecostan form of the young on Plate XXXIV., and in Fig. 4-6 the 

 adult of Androgynoceras hybridum, his JEgoceras heterogeneam. A more accelerated 

 form is shown on Plate XXXV. Fig. 4-6, in which the young are similar to 

 lateecosta for a less prolonged period of their growth. "Wright's JEgoc. Henleyi, 

 Plate XXXIII., is also a specimen of the same species with a prolonged latse- 

 costan stage of growth. Lip. Henleyi, figured by Wright as JEgoc. striatum, 

 Plate XLIII., is also highly accelerated, and most of the specimens have young 

 shells with no traces of their latsecostan ancestry, reproducing only the char- 

 acteristics of the adult whorls of And. hybridum. Lip. Bechei, also figured by 

 Wright, Plate XLIL, is still more accelerated in its mode of development, since 

 the young has no resemblance to the adult of And. hybridum. From the smooth 

 stage of the nsepionic period of growth it passes abruptly to a stage in which the 

 shell resembles the adult form of And. Henleyi. The whorls at this stage show 

 the specific characters of the adult of And. Henleyi; they are too involute and 

 too heavily ribbed and tuberculated in proportion to their size to be compared 

 with the adult of And. hybridum. 



Wiirtenberger's book is devoted to the exposition of this law of heredity 



1 Paleontological Soc, XXXII., 1S78. 

 G 



