98 PROTOZOA. 
GYMNOMYXA AND CORTICATA. 
The Protozoa fall into two fairly well-defined Phy/a, in 
accordance with an important character. In the Gym- 
nomyxa the body of the animal consists of naked protoplasm 
which has no definite shape of itself. In many cases the 
protoplasm has a shell to which it clings, inside or outside 
of it, and under tonic contraction or when the vital 
processes are dormant it assumes a spherical shape. The 
nakedness of the protoplasm implies a very low differentia- 
tion, the alimentary functions of ingestion and egestion being 
co-extensive with the surface (cf Ameba). In the Corti- 
cata the living organism assumes a definite shape, which is 
maintained by a hardened cortex and often a cuticle as 
well. The form of the body is not determined each 
moment by the forces acting upon it, but a definite shape or 
plan is assumed and adhered to for each species. A 
definite mouth, definite egestive spot and definite motor 
organs are involved. The Corticata are evidently a great 
step in advance of the Gymnomyxa, from which apparently 
they have been derived. 
PHYLUM GYMNOMYXA. 
Fig. 32,—TyPES OF FORAMINIFERAN SHELLS (After D’ORBIGNY) 
ia 
Uvigerina. Bulimina. Calcarina. Peneroplis. Planorbulina. 
