A. Hyatt—Biological Relations of the Jurassic Ammonites. 847 
an embryonic condition in the young of the Jurassic Am- 
monites. 
It also accounts for the inheritance of the more and more 
involved form in each of the subordinate series. This becomes 
apparent when the parallel forms of any series are traced from 
the primary discoidal or open umbilicated through the inter- 
mediate forms to the most completely involved. 
We find in all cases the more discoidal or primary with all 
its characteristics, whatever they may be, repeated at earlier 
stages in each species, until at last in some of the most invol- 
ved, all perceptible traces of its existence are lost. Then and 
only then can the series be said to die a natural death. When 
this form appears I have never found another. The rea- 
son for this is that in all cases the disappearance of the pri- 
mary or ancestral form and characteristics of the series is due 
a greater or less period of time under the influence of physical 
surroundings. : 
The word surroundings is now used instead of environment, 
for the reason that environment covers the whole ground of 
physical causes which may have either a remote or immediate 
&ct upon the life of the species. : 
The environment, or the sum of the physical influences, how- 
ever favorable it may seem to be, is, as is well known to all 
