74 
of muscular movement disappears; and in a 
‘short time they become collected in small 
groups or clumps, as a result of their inability 
to effect the muscular movements necessary to 
disengage them from the contact and adhesion 
of other larve. The fact that ciliary activity 
can continue (in some cases for many hours) in 
solutions in which all muscular movement is 
impossible, proves that these two forms of con- 
tractility are essentially very different. 
Solutions containing three salts in suitable 
proportions are much more favorable than 
those containing only two. In solutions of the 
composition 40 cc. 5/8n NaCl + 55 ce. 10/8n 
MgCl, + 5 ce. 10/8n CaCl,, larvee may remain 
living and capable of growth for so long a period 
as two weeks. Mixtures of the above three 
salts are the most favorable; the presence of 
KCl is injurious since potassium acts as a spe- 
cific poison on muscular tissue. The three most 
essential metallic ions for the life-activities of 
these organisms are apparently Na, Ca, and 
Mg; K in very small proportions is probably 
also necessary. 
On analysis of the normal swimming move- 
ments of the larvee it appears that ciliary 
and muscular movements play separate and 
independent parts. Propulsion is effected ex- 
clusively by the action of the cilia, while 
heliotropic orientation is a purely muscular 
phenomenon with which the cilia have nothing 
directly to do. That this is so is proved (1) by 
direct observation, which shows that the cilia 
never exhibit a greater degree of activity on 
one side of the body than on the other, while 
the muscles of the more strongly illuminated 
side always show stronger contractions than 
those of the other ; (2) by the fact of heliotropic 
orientation of the larve in later stages after 
the cilia have disappeared; and (3) by the fact 
that all power of heliotropic response is lost in 
solutions that remove muscular contractility 
without at first interfering with ciliary move- 
ment. C. M. CHILD, 
Secretary. 
ZOOLOGICAL JOURNAL CLUB OF THE UNIVER- 
SITY OF MICHIGAN. 
THE meetings of November 6th and Novem- 
ber 13th were occupied by Dr. H. 8. Jennings 
SCIENCE. 
[N.S. Von. XIII. No. 315. 
with an account, accompanied by demonstra- 
tions, of his researches on the activities of 
unicellular organisms. By means of the are 
light, stereopticon and projecting microscope, 
with an intervening alum cell to cut out the 
heat, the living organisms were projected on the 
screen, and their reactions to various stimuli 
could be observed by those present. Parame- 
ciwm thus appeared three inches long, and its 
minute structure, even to the cilia, was vis- 
ible. 
The collecting (‘positive chemotaxis’) of 
Paramecia about a bubble of CO, and in solu- 
tions of mineral acids was shown; also the 
spontaneous collections formed by the organ- 
isms, owing to the presence of CO, excreted by 
themselves. ‘Negative chemotaxis’ toward 
salt solutions was shown in the same way. 
Attention was then directed to the mechanism 
of the reactions, and it was pointed out that 
there was no orientation of the organisms either 
in collecting in the acids or in the negative re- 
action to salts. By throwing on the screen a 
slide of Paramecia with a small ring marked on 
the outside of the cover-glass, it was shown that 
in their swift roving movements at least ten 
Paramecia per second crossed this ring ; hence 
that if any method could be found of keeping in 
the ring those that crossed it by chance, the 
area would soon swarm with the Paramecia. A 
drop of weak acid was now introduced beneath 
the marked ring; it could then be observed 
that the animals swam into the area just as be- 
fore, but that on coming to the outer boundary 
of the area, they were turned back. Hence 
every Paramecium entering by chance remained 
in the area—swimming rapidly from one side 
to the other—and in a short time a dense col- 
lection was here formed (‘positive chemo- 
taxis’). 
To show the exact mechanism of the reac- 
tions, an organism having a more differentiated 
structure, so that its movements could be more 
easily followed, was thrown on the screen. 
For this purpose Oxytricha was used. The 
differentiation of right and left sides in this in- 
fusorian was pointed out; then as the individ- 
uals approached a source of stimulus, the lec- 
turer predicted, by pointing, in which direction 
the animal would turn on arriving at the stim- 
