

WHAT IS BATHYBIUS ? 651 
much patient labor to characterize those that are truly spe- 
cies and those that are varieties only. 
EXPLANATION OF PLATE 1l. 
Fig. i: spar dip — Say. Lake Champlain to Bi ts 
ig appressa Say. Northern a to Pac 
1 í ds hs phs Northern Stat 
pu T x decollata Mighels. Maine, M E 
sn. dE proxima Lea. California. 
MEE S de n Jay. Lake Champlain to Michig: 
Figs: 7, 8, 9; 10, 2. Lymnea elodes Say. Northern Unita States. 
Fig. 18. Lymnea decim Say. New England to Kansa 
Figs. 14, 15, 16, 17, 18, 19. Lymnea columella Say. Mew England, Lake 
Superior, Georgia. 
Fig. 20. Physa ampullacea Gould. Or -— 
ék 
21. **  Virginea Gould. Calif 
w. 92. “ Lordi Baird. British ks 
dip NM. E gem a Say. Northern ud sd figured from origi- 
nal spec 
id 24. Thie iaio Say. Northern United Sta 
25o S mop Say. Throughout ak States. 
SP Og Oe Animal expanded. 
* 27. ** humerosa Gould. Colorado De esert 

WHAT IS BATHYBIUS ? 
BY PROFESSOR W. C. WILLIAMSON, F.R.S. 

DuniNG each successive year the Protozoa prove to be of 
increasing importance to the physiologist. In no other class 
of matured animals can the protoplasm, of which we have 
recently heard so much, be studied to such advantage. Con- 
stituting the lowest known manifestation of both animal and 
vegetable life, it seems to bring us very near to the boundary 
between the organic and the inorganic worlds. It exhibits 
the simplest phenomena of life under the least complex of 
-eonditions; hence it has recently been appealed to by one 
of the most philosophical of living zoologist as capable of 
