ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 211 



— are specially modified individuals whose function is to give rise to 

 new colonies. Conjugation was not observed. 



Movements of Flagellata and Ciliata* — Mr. H. S. Jennings has 

 extended to a number of infusorians the experiments (previously re- 

 ported on) which he made on Paramsecium, and the general result is 

 to show a similar " motor reaction plan " throughout. The more im- 

 portant conclusions are the following. 



The motor reactions to stimuli in the Flagellata and Ciliata take 

 the form of a reflex of definite character, the usual features of which 

 arc that the animal moves backward some distance, turns toward a 

 structurally defined side, then moves forward. 



This motor reflex is produced by chemical stimuli of all sorts, by 

 fluids active through their osmotic pressure, by heat, by cold, and by 

 mechanical shock ; in fact, by all agents capable of causing a motor 

 reaction. 



The direction of motion throughout this reflex has to only a very 

 limited degree a relation to the localisation of the stimulus. The direc- 

 tion of turning is determined by structural differentiations only, but 

 whether motion shall take place backward or forward along the body- 

 axis is to a certain extent determined by the localisation of the stimulus. 

 The general effect of this reflex is to remove the organism from the 

 sphere of influence of the agent causing the reaction, and to prevent it 

 from re-entering. 



Chemotaxis is not passive attraction or repulsion, but an active 

 movement due to the production of this motor reflex by the chemical 

 agent in question. There is no such thing as direct attraction or 

 repulsion shown by these animals. They leave certain areas vacant 

 because influences in these areas cause the motor reflex ; they gather 

 in certain areas when the conditions within these areas are not such 

 as to cause the motor reflex, while the surrounding influences do 

 cause it. 



The motor reflexes through which the reactions are produced are 

 of the same order as the motor reflexes in higher animals. But the 

 behaviour of the infusorians shows them to occupy an extremely low 

 place in the psychological scale, most of their activities being due to a 

 single reflex. There is evidently no immediate analogy between the 

 reaction movements of these unicellular organisms and the growth move- 

 ments of higher forms ( t; tropisms "), so that the phenomena shown by 

 the former do not justify the drawing of direct conclusions concerning 

 the latter. 



Conditions of Conjugation in Infusorians.f — Prof. E. Hertwig has 

 made experiments which show that chromatin-reduction is induced both 

 by starving and by over-feeding. In more general terms, a condition 

 favouring the occurrence of conjugation is disproportion between nuclear 

 and cytoplasmic mass. 



Observations on Euglena gracilis. J — Herr Hans Zumstein finds 

 that this form can thrive in either autotrophic or heterotrophic fashion, 



* Amer. Journ. Physiol, iii. (1900) pp. 229-60 (15 figs.)- 



t SB. Ges. Morph. Physiol. Miinchen, 1899, 8 pp." See Zool. Centralbl., vii. 

 (1900 1 pp. 44-5. 



% Pringaheiin's Jahrb. f. wiss. Bot., xxxiv. (1S99) Dp. 149-9S (1 pi.). 



