ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
495 
Trochospongilla horrida, Ephydatia fluviatilis, and E. miilleri — to which 
must be added Carterius stepcmowi for eastern Europe. The other 
species are localised in widely separate haunts, and may be regarded as 
secondary. 
Ephydatia bohemica Petr.* — Dr. Paul Girod gives reasons for 
transferring this species to the genus Carterius, and suggests that further 
investigation may show its identity with C. stepanoivi. 
Protozoa. 
Physiology of Paramsecium.f — Mr. H. S. Jennings, in the course 
of his observations on the reaction to stimuli of unicellular organisms, 
has made some interesting experiments on the motor reactions of Para- 
msecium and their mechanism. He finds that this organism has a single 
motor reaction by which it responds to all classes of stimuli. The 
reaction is such that the direction of movement is reversed, the animal 
is driven backward, and then swings round to the aboral side. When 
a change of direction has been thus accomplished, the animal returns to 
the ordinary forward movement. The intensity of the different parts 
of the reaction varies with the intensity of the stimulus. The reaction 
occurs in the same way whether the stimulus acts on a special part of the 
organism or on the whole surface at once ; that is, Paramsecium does 
not turn directly towards a beneficial source of stimulus or away from 
an injurious one, but has one method of reaction determined by its 
structure. The terms positive and negative taxis cannot strictly be 
applied to Paramsecium , for it cannot be said to be directly attracted or 
repelled by certain agencies or conditions. The swarming near bene- 
ficial sources of stimuli is not active, but is due to the fact that these 
sources cause no motor reactions. In general the movements of Para- 
msecium seem to be merely the result of its power of responding to 
a stimulus by one fixed and definite reaction. 
In another paper the author considers the laws of chemotaxis in 
Paramcecium, the expressions positive and negative chemotaxis being 
used not in any exact sense, but merely to designate the results produced 
by attractive or repellent substances when introduced into the medium 
in which the organisms are living. He finds that chemotaxic substances 
produce the same motor reactions as mechanical shock or any other 
stimulus, and that this motor reaction is the same whatever the position 
of the reagent or of the organism, so that a chemical which, acting on 
the anterior end of the organism produces positive chemotaxis, will 
produce negative chemotaxis when acting on the posterior end. The 
organisms are most nearly at rest in a weakly acid solution, and collect 
in weakly acid solutions ; hence their positive chemotaxis towards nutri- 
tive substances such as meat extract. The chief factor causing the motor 
reaction which results in negative chemotaxis, is not the injuriousness of 
the substance, but is of a chemical nature, equally injurious substances 
not having equally repellent powers. 
Fresh-water Protozoa.^ — Dr. Robert Lauterborn describes a number 
of new or little-known forms. In a pond at Maudach he found a curious 
* Bull. Soc. Zool. France, xxiv. (1899) pp. 54-6. 
f Amer. Journ. Physiol , ii. (1899) pp. 311-40 (15 figs.) and 355-79. 
X Zeitschr. f. wiss. Zool., lxv. (1899) pp. 369-91 (2 pis.). 
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