THE VITAL PROPERTIES OF THE CELL 



303 



rotating on its own longitudinal axis. After this had been going 

 on for several minutes, and had been repeated with several fixed 

 individuals one after the other, the bud at last attached itself to 

 one of them, generally at the aboral end, near the stalk. After a 

 few minutes the fusion might be definitely observed to be taking 

 place." 



In connection with the above-mentioned description, Engelmann 

 remarks : " At another time I observed a still more striking 

 physiological or even psychophysiological exhibition. A free bud 

 crossed the path of a large Vorticella, which was travelling with 

 great rapidity through the drop, and which had abandoned its 

 stalk in the usual manner. At the moment of meeting, although 

 there was absolutely no contact, the bud suddenly changed its 

 course, and followed the Vorticella with the greatest rapidity ; then 

 a regular chase ensued, which lasted for about five seconds. 

 During this time the bud kept at a distance of about -^ mm. 

 behind the Vorticella however, it did not succeed in overtaking 

 it, but lost it in consequence of its making a sudden side move- 

 ment. Hereupon the bud continued its path at its original slower 

 pace." 



This phenomenon of influence exerted at a distance has also 

 been observed by Fol (VI. 19 a) in animal cells, such as the ova of 

 the Star-fish. Each ovum is surrounded by a thin gelatinous 

 envelope. When fresh spermatozoa of the same species approach 

 the surface of the envelope, the one which is most in advance 

 exercises a distinctly perceptible influence upon the yolk (Fig. 160). 





FIG. 160. A, B, C Sections of ova of Asterias glacialis, after Fol. The spermatozoa have 

 already penetrated the gelatinous envelopes of the ovum. In A, a prominence is just 

 beginning to rise up to meet the most advanced spermatozoon. In B, the promin- 

 ence and spermatozoon have 1 met. In C, the spermatozoon has penetrated the egg which 

 has formed a yolk-membrane with a crater-like aperture. 



