LIFE HISTORY OF TWO RARE CILIATES 359 



was 3.1, the lowest rate of division for the same series for a simi- 

 lar period of time being 0.2 per day. Averaging the high and 

 low division rates of the three hnes from February 24 to July 7, 

 1911, a division rate of 1.5 in twenty-four hours, was found. 



Division of the cell and macronueleus is preceded by their 

 gradual elongation, this continuing until the cell has nearly 

 doubled its length, in fact in some cases the dividing cell exceeds 

 twice the length of the vegetative cell. 



The variation in form of the macronueleus in division is inter- 

 esting. Sometimes it is simply folded upon itself, appearing 

 like a single strand except at the point where the two ends sepa- 

 rate (figs. 23, 24 and 25); again two distinct pieces may be 

 distinguished, each one folded upon itself and the parts inter- 

 twined (fig. 26). Sometimes an exaggerated elongation of the 

 nucleus occurs as shown in figure 27, in which it is extremely 

 difficult to follow the coils and intertwinings. 



After the elongation of the cell is accomplished a constriction 

 occurs half-waj^ between the anterior and posterior ends, a new 

 vacuole appearing anterior to this infolding. A little to one 

 side of the point of attachment of the dividing cell, a new mouth 

 is formed in the posterior cell. The position of the new mouth 

 is best seen in the living organism immediately after division. 

 The constriction increases until the cell and the nucleus are 

 divided into approximately equal parts as shown in figures 29, 

 30 and 31, although an occasional exception is found where 

 the larger part of the nucleus lies in the anterior cell (fig. 28). 



During the process of division Spathidium swims slowly about, 

 but during the later stages its activity increases. It not only 

 swims more rapidly but it twists the anterior end so energeti- 

 (ially that the connection between the two cells is reduced to a 

 delicate strand, this condition continuing for an hour or more. 

 When the slender thread of tissue is severed, the anterior cell 

 swims rapidly away, leaving the posterior half rotating slowly. 

 The posterior individual is at first ovoid in form, the anterior 

 end marked by the new mouth placed somewhat obliquely, 

 the posterior end by the original vacuole. Soon the rotary 

 motion ceases ; the new cell swims slowly about, increasing gradu- 



