548 THE AMERICAN NATURALIST.  [Vor. XXXIX. 
cellular organisms seem to present the simplest conditions and 
examples for the expression of the various laws of development 
that can be found anywhere in the animal kingdom. 
Loss OF ORNAMENTATION. 
Ridges. —In a specimen of Uvigerina angulosa Williamson, 
var. spinipes Brady (Fig. 16), the e chambers have definite 
raised coste or ridges run- 
ning generally parallel to the 
axis of the growth of the 
shell. In later growth this 
character becomes less pro- 
nounced and in the last five 
chambers which by measure- 
ment represent more than 
half of the growth, is entire- 
ly wanting, and the cham- 
bers are perfectly smooth. 
Although not included in 
this family, Bulimina sub- 
ornata Brady is figured here FtS- :6— Uvigerina angulosa Williamson, var. 
(ur a f ak viij Brady, showing loss of ornamentation 
parison shows n senesce 
in much the same manner Fis. 7 Blinn seid Pe een 
(Fig. 17) the costate early 
growth and the gradual disappearance and final loss of costation 
in the old age of the individual. 
Tubercles.—ln Cristellaria echinata d'Orb. (Fig. 18), the early 
growth is marked by rows of bead-like tubercles over the sut- 
ures, while the intermediate space is covered with hemispherical 
granules. In later growth these scattered granules are limited 
to the peripheral portion and on the last two chambers are 
entirely wanting, so that the surface of these chambers is 
smooth. The rows of bead-like tubercles also disappear in old 
age and pass into a smooth ridge. Similar conditions are 
found in various groups of the Mollusca, especially in certain of 
the fossil Trigonias. In such forms the costae break up into 
knobs and bosses in development, and later in the old age of 

