CATAGENESIS. 77 



of heredity, that like tends to reproduce like, cannot be assumed with regard to the transmis- 

 sion of senile characters, since these ivere probably not directly transmitted from one species to 

 another. Nevertheless, the tendency to degeneration must have been inherited, if ive can 

 judge by the appearance of retrogressive characters at earlier stages in successive species. 



In the three geratologous series, Asteroceras, Agassiceras, and Oxynoticeras, 

 we find the same laws of anagenesis and catagenesis. The psiloceran-like or 

 progressive species were the immediate progenitors or proximate radicals of 

 progressive varieties, species, and genera in the direct line of descent, but when 

 geratologous forms began to appear, and progression changed into retrogression, 

 there was a corresponding change in the radicals. Then the retrogressive forms 

 arose from varieties which were themselves also proportionately degenerate, and 

 had similar retrogressive and geratologous characters. 



The progressive stage with divergent sides and broad abdomen, which 

 appeared in the young of Ast. oblusum and was found in some adults, was 

 suppressed, and was replaced by a modified quadragonal form in Ast. Turneri. 

 This in turn was replaced by the tendency to accelerate the development 

 of the trigonal convergent-sided whorl and its correlative retrogressive charac- 

 ters, the untuberculated pilse, low broad keel, and shallow channels, in Ast. Brooki, 

 impendens, and denotatum. The geratologous trigonal form appeared at an earlier 

 age in each successive species, until at last in Ast. Collenoti 1 it took possession of 

 the earliest nealogic stages. 



The retrogression of form in the series of species may often be compared 

 with parallel pathological series of individuals, which may be made within a 

 single species. Ast. stellare 2 had dwarfed forms, much smaller than most of the 

 healthy adult specimens of its own species. These last, though so much larger, 

 ordinarily showed no signs of old age, while the dwarfs were completely changed 

 by senile metamorphoses. Much smaller but similarly dwarfed specimens oc- 

 curred in Ast. acceleratum, with even more compressed and prematurely aged 

 whorls. 3 A remarkable series of these dwarfs, from which the two figures 

 referred to in the notes were drawn, is to be found in the Museum of Stutt- 

 gardt. The smallest of these completely geratologous specimens is not over 

 half the size of the largest, which itself is not of average size, as stated above. 

 The comparison of these dwarfs with the more involute varieties of Ast. Brooki 

 and the adult of Ast. Collenoti shows that they cannot have been connected by 

 direct inheritance. They were evolved independently of these geratologous 

 forms, and I am not calling upon the imagination to fill any blanks when I 

 speak of them as homoplastic morphological equivalents of Ast. impendens and 

 Ast. Collenoti. It can hardly be doubted that the geratologous forms, when 

 found as dwarfed varieties within a species, are the products of the unfavorable 

 action of the surroundings, or, in other words, that they are more or less dis- 

 eased individuals. Their close parallelism in every respect with Ast. Brooki, 

 impendens, and Collenoti shows that we can attribute with great probability the 

 origin of all such forms to similar pathological causes. 



With regard to the agassiceran series, it may be remarked that the quad- 



1 PI. ix. fig. 10-11 b; pi. x. fig. 10. " PI. x. fig. 1, 2. 3 PI. x. fig. 3. 



