236 REVIEWS. 
proved, we think, by the fact that degradational or senile tendencies are 
inherited. 
In this connection I — suggest that the Turrillites and other allied 
spiral shells, will ultimately be found to be the legitimate descendants of 
the defo aed Tur prm described by D'Orbigny from the Lower Lias 
beds. It is now generally xni oi ER y European writers that these 
forms are discoidal ammonites that have di cid from the usual mode 
of growth common to their Sueco, and instead of revolving neue in 
the same plane the whorl has become slightly assymetrical, and thus be- 
gun to form the assymmetrical spiral of the genus Turrillites. This 
tendency is quite common with the septa of Psiloceras psilonotus eem 
other species, and in.the shell, also, but is so faintly See that i 
difficult to distinguish from the effects of compression. If this and a 
instances of a similar kind be finally substantiated we have are still an- 
other application of the law of acceleration > See ae which 
naturalists have been hitherto accustomed to c deform 
prolong their existence by perpetually inheriting the a senate s of their 
ancestors, and certainly the degradational characteristics as displayed in 
all the terminal species of the ammonoids cannot be explained in this 
wa; ere also we have the limitation of the cycle of changes or varia- 
Mond which a species or form may be supposed to be capable, at least 
part sin accounted for; and as Professor Dawson and others have 
pointed out, the theory of natural selection makes no provision for such 
restrictions rsion cannot be called upon to Born the return of 
the Nautiloid forms i onoids of the Cre $ boenus they 
8 the t of traceable inherited characteristics continually aug- 
naL T 
or atrophy of the adult ac in the individual, and in the group, 
by an unrolling of the closely coiled and deeply involute whorl of the 
Jurassic ore es, and they occupy the — extreme of structure and 
life in both c 
d Mii in ipee that Professor Dawson does not wholly 
commit himself to the new theory, but regards it as ** holding forth the 
most promising line ss investigation" as yet advanced. Though the 
author of the theory in common with Professor Cope, we cannot refuse to 
until the extent to which it may be modified by physical causes, and per- 
haps natural selection, be fully understood, an unprejudiced mind cannot 
consider it as capable of clearing away all our present difficulties. It 
gives us, perhaps the means of asserting that the plasticity of organs 
