peesident's address. 277 



a close resemblance to the ancestral Goniatites. With growth the 

 septa and their sutures show successively greater and greater complexity 

 till the well-known foliaceous appearance is presented. The exterior 

 of the shell will also show gradations in its sculpture : the 

 smooth surface of the young Ammonite will develop ribs which, as 

 growth proceeds, become more and more complex, while to the ribs 

 spines may be added. In other forms again the sculpturing of the 

 adolescent, or of the adult shell, gradually disappears with age, the 

 test reverting to a smooth condition. 



The individual, therefore, presents in itself a history of its descent, 

 and so to a certain extent of its race. To a certain extent, because 

 Hyatt further found and was the first to point out that there was 

 a tendency, not merely sometimes, as Darwin supposed {20, p. 10), 

 but constantly, for the higher forms to reproduce the characters of 

 their predecessors at earlier and earlier stages in their development. 

 " The young of higher species are thus constantly accelerating their 

 development and reducing to a more and more embryonic condition, or 

 passing entirely over, the stages of growth corresponding to the adult 

 periods of preceding or lower species" {SIj., p. 203). 



This he denominated the 'Law of Acceleration,' or ' Tachy- 

 genesis ' {SIj., IfO-2). These phenomena of Ontogenesis, Phylogenesis, 

 and Tachvgenesis were also independently discovered by Wiirtenberger 

 {62) andBuckman(5, 12). 



How these principles apply in the phylogeny of the Ammonites 

 will best be shown bv the following quotation from a paper by 

 Professor J. F. Blake \5, pp. 280-1):— "If we want to know the 

 nearest ancestor of a form A, we must find a form B which reproduces 

 in the adult the early whorls of A ; in the same way C, the immediate 

 ancestor of B, must reproduce its [B's] early whorls ; and so the 

 series grows. It may, however, often happen, on account of the 

 acceleration, or even abbreviation by curtailment, of development, 

 that the early whorls of the latest, A, do not show us the stages so 

 far back in the history, even on a diminished scale, as the early, 

 or even the later, whorls of C ; and so it might be proved, step by 

 step, that a form which, neither in its adult stages nor in any earlier 

 stage agreed with a second, might yet be of the same lineage. In 

 this way a well-proved lineage may pass from so-called species to 

 species, from so-called genus to genus, and from so-called family 

 to family." 



Moreover, this process of development takes place not merely in 

 a direct line, but along lines branching, as it were, from some original 

 primitive form. 



The genetic relationships among the Ammonoidea have been the 

 subject of many memoirs. The principal writers, beside Hyatt {o!^-l^2), 

 have been S. S. Buckman {8-11), Haug {30), Karpinsky {Ij.3a), 

 Waagen {59), Wiirtenberger {62-3), and to their writings the student 

 must turn. 



One other contribution to the study of evolution as exhibited in 

 the Cephalopoda claims attention, viz. Hyatt's contention that the 

 group affords proof of the inheritance of an ac(2uircd characteristic. 



