LIFE HISTORY OF TWO RARE CILIATES 365 



(e) No evidence has been found in Spathidium of a differ- 

 entiation of nuclear material into a macronucleus and a micro- 

 nucleus. The macronucleus, a greatly elongated cylindrical 

 organ, sinuous in outline and intricately coiled, possesses a 

 delicate membrane within which lie closely crowded chromatin 

 granules, surrounded by a faintly staining substance. Division 

 of the chromatin masses has been observed in sections of early 

 division stages. 



(f) Division of the organism is preceded by an elongation 

 of the body and nucleus ; a constriction appears half-way between 

 the anterior and posterior ends; a new vacuole forms anterior 

 to the constriction, a new mouth, posterior to it and a little to 

 one side of the median line of the dividing cell. 



(g) Encystment takes place under unfavorable environmental 

 food and temperature conditions. The free swimming forms 

 can be recovered by bringing about normal conditions of environ- 

 ment in respect to food, temperature and quantity of liquid. 



(h) Conjugation was not observed, although numerous at- 

 tempts were made to bring it about. 



(i) The descendants of a single individual of Spathidium 

 were followed through 218 generations extending from February 

 24, to July 7, 1911, variations in division rate being graphically 

 represented by a plotted curve. This curve, showing the divi- 

 sion rate of the protoplasm, illustrates the normal rhythms 

 described by Woodruff. 



II. ACTINOBOLUS RADIANS 



1. History 



Stem observed this rare and interesting organism among the 

 filaments of fresh-water algae in standing water. His descrip- 

 tion, limited to a footnote in the second volume of '*Der Organ- 

 ismus der Infusionsthiere," is as follows: 



Diese neue Gattung beruht auf einem merkwlirdigen Thiere, welche 

 ich seit mehreren Jahren bei Niemegk ziemlich haufig in stehenden 

 Gewassern zwischen der vielwurzeligen Wasserlinse beobachtete und 

 welches ich Actinobolus radians nennen will. Der Korper ist fast 

 kugelig oder umgekehrt eiformig, am vorderen Pole mit einem kurzen 



JOURNAL or MORPHOLOQY, VOL. 23, NO. 3 



