441 
wholly to fill. In short a Heliozoon differs from Protomyza (over and 
above its possession of a nucleus) merely in the excessively high diffe- 
rentiation and relative permanence of the amoeboid stage of its life 
cycle: the Monad or the Infusor has similarly developed its ciliated 
stage, the Myxomycete its plasmodial. In the Protophyta the resting 
or encysted stage certainly predominates, but they too show phases of 
the same life cycle, as the naked motile zoospores of so many Fungi 
and Algae (which as »a transition from plant to animal lifec so per- 
plexed the elder Botanists) and, the amoeboid stage into which these 
so often collapse, bear witness. 
This view at once demonstrates the thorough unity and natural- 
ness of the Protista, and affords a basis for their classification into series 
corresponding to the stages of the life-cycle. In the Palmellaceae or 
Schizomycetes the resting and motile stages are almost equally promi- 
nent, while in the Desmids and Diatoms and the Saccharomycetes the 
encysted stage predominates. The Protoplasta, the Foraminifera, the 
Heliozoa and the Radiolaria are of course referable to the prepondera- 
tingly amoeboid type, while the Infusoria represent the ciliated. The 
Myxomycetes far from having any relations to the Fungi stand on the 
whole nearest to the Moneron or Protomyxoid type, despite the ex- 
cessive differentiation of their plasmodial stage. 
Huxley has called attention to the importance of the alternation 
between the amoeboid and ciliated stages which he terms Myxopod and 
Mastigopod (Anat. Invert.) and Lankester has divided the Protozoa into 
Gymnomyxa and Corticata (Quart. Journal Microsc. Sc. XVIII); the 
present proposal includes both points of view. 
_ Leaving the details of this classification to the completed paper 
let us consider the physiological aspects of this cycle. A mass of pro- 
toplasm is under constantly varying conditions, at one time receiving 
abundant energy — heat and food — from the environment, at another 
little or none, and thus a rhythm of more and less vital activity ensues. 
The amoeboid state, as every observer knows, varies extremely with 
food and temperature: Haeckel and others have shown that the cilia- 
ted stage is merely an exaltation of the amoeboid, and the cilium but 
a rhythmically contractile pseudopodium, while on the other hand the 
ciliated cell may coliapse into an amoeba and the active Amoeba sink 
gradually into a quiescent spheroidal mass. 
Vast importance has been attached to the cellulose wall as an 
assumed characteristic of plants, yet the coat of an Amoeba or of a My- 
xomycete is known to be composed of cellulose. Contracting muscle 
evolves much carbonic acid and water, with evolution of heat. Con- 
tractility implies waste; if contractility ceases these waste products will 
