HUXLEY, ON CLASSIFICATION. 79 
then, quite suddenly, shuts again. After a little time the same 
diastole and systole are repeated. As the systole takes place, it is 
possible, occasionally, to discern certain radiating canals, which 
extend from the cavities into the surrounding sarcode, and disappear 
again before diastole occurs. There is no doubt that the clear space 
is a chamber filled with fluid in the cortical layer, and since good 
observers maintain that there is an aperture of communication, 
through the cuticula, between the ‘ contractile chamber’ and the ex- 
Fie. 4. 
Wi 
od 
iW 
Fig. 4. Paramecium bursaria (after Stein). A, the animal viewed from the 
dorsal side; @, cortical layer of the body; 4, ‘‘nucleus;” c¢, contractile 
chamber; d, d’, matters taken in as food; e, chlorophyll granules, 
B, the animal viewed from the ventral side; a, depression leading to 4, 
mouth; ¢, gullet; d, “‘nucleus;” d@ “nucleolus;” ¢, central sarcode. In 
both these figures the arrows indicate the direction of the circulation of the 
sarcode. 
C, Paramecium dividing transversely; a, a’, contractile spaces; 4, J’, 
“nucleus” dividing; ¢, c’, ‘‘nucleoli.’’ 
terior, this fluid can be little more than water. Perhaps the whole 
should be regarded as a respiratory or secretory mechanism : in one 
shape or another, it is eminently characteristic of the Infusoria. 
Besides this singular apparatus, there lies embedded in another part 
of the cortical layer a solid mass, of an elongated oval shape (Fig. 4, 
A B d), which has been called the “nucleus,” though it must be 
carefully distinguished from the “nucleus” of a cell. Upon one side 
