1893.] Phylogeny of an Acquired Characteristic. 865 
PHYLOGENY OF AN ACQUIRED CHARACTERISTIC. 
By ALPHEUS HYATT. 
An acquired character is a modification which makes its 
appearance in the adult or later stages of development and is 
obviously dependent for its origin upon other than hereditary 
causes. I have elsewhere defined that branch of science which 
deals with such problems as Ctetology:and such characters as 
ctetic or acquired. The characteristic dealt with in the paper of 
which this is an abstract, is of essential importance among 
Nautiloids and Ammonoids or all of the Cephalopoda having 
chambered shells and living within their shells. It consists 
mainly of an impression made on the inner side or dorsum of 
each outer whorl during the coiling up, as the whorl grows 
and is moulded over the venter or outer side of the next inner 
horl. 
This matter will be better understood, if a short description 
is given of the following figures. Figs. 1-2 show an almost 
