1876.] 383 [Hyatt. 



these are due to similar causes, disease, either normal or abnormal, 

 produced by the continued action of unfavorable surroundings on the 

 individual. That old age is a normal disease, or that it at least should 

 be classed with pathological phenomena, can hardly be questioned. If 

 it were questioned, however, the similarities between distorted forms 

 occurring in unfavorable situations and the normal retrogressive 

 changes of old age in a well formed individual of the same series, 

 would settle the dispute; the products of the direct action of disease 

 produced by unfavorable surroundings, and often even by wounds and 

 those due to senility have a wonderful similarity. These senile char- 

 acteristics may appear, as in Steph. Bayleanum, as probably the result 

 of the direct action of certain unknown, but unfavorable causes, upon 

 the organization of nodosum, or only slightly, as in Steph. Humphrie- 

 sianum or not at all, as in Steph. Blagdeni, which as a descendant of 

 Steph. subcoronatum ought, unless sustained by some exceptionally 

 favorable surroundings, to show decisive marks of senility. This case, 

 and that of Steph. macrocephalum previously cited, show that the nor- 

 mal retrogressive tendency of old age may occasionally be to some ex- 

 tent counteracted by the process of growth, as shown by the increase 

 in growth of the shell, even in old age, of these two species. This, of 

 course, can only be attributable to some exceptionally favorable cir- 

 cumstances, which for a time give extraordinary power to the organ- 

 ization. But this is only for a time, since in all series having a pro- 

 longed existence, old age forms eventually make their appearance 

 just as senile characteristics do in the individual. 



Wherever the old age or diseased tendencies make their appear- 

 ance they tend to the production of similar forms. If mitigated by 

 the very favorable circumstances under which the race is living, and 

 the shell, in consequence of the unimpaired powers of assimilation of 

 the animal, continues to increase proportionally in size and in the 

 involution of the whorls throughout life, we find that a narrow- 

 abdomened, convergent-sided and very involute whorl is evolved in 

 the last or highest members of the series, whether it comes from the 

 round abdomened, or the keeled or channelled groups. If, however, 

 the surroundings are not especially favorable, and the assimilative 

 powers become impaired, as shown at first by the decrease in size of 

 the whorl in the old age of the individual, then all degrees of irregu- 

 larity in the whorl become manifest in the last or highest members 

 of the series, tending to the production of Scaphitoid forms. 



This, in many series, is probably due to the direct inheritance of the 



