^QO H. S. Jennings 



was observed, and its history followed for many generations. 

 The observations on this structure likewise give certain important 

 results as to the method of growth in Paramecium. 



First generation. The ancestor of the race we are to study was 

 a crooked individual (Fig. 3, a), found in a culture containing 

 many specimens, where food was getting scarce. I have called 

 this individual a\ we shall use this designation for the race as a 

 whole, appending certain exponents to indicate the various mem- 

 bers of the different generations. The anterior individual result- 

 ing from fission will be designated by the exponent (^), the posterior 

 individual by the exponent (^). 



The original individual a was bent just in front of its middle at 

 practically a right angle (Fig. 3, a). It was isolated at 2.50 p.m., 

 May 2, 1907. 



Second generation. The first division, during the night of May 

 2, showed that the crookedness was not to be inherited, though 

 it had its effects on the progeny. The animal divided transversely, 

 posterior to the bend in its body. The posterior product (<3^) 

 was normal in all respects, so that it need not concern us further. 

 The anterior product {a^) was of about the form that would be 

 expected from dividing a behind the bend in its body, save that 

 the posterior end had become still more irregular. This end was 

 broad and truncate; nearly triangular when seen from the rear; 

 it extended backward at two of the angles as two pronounced 

 points (Fig. 3, ^). 



Shortly after division the daughter individual a^ changed shape 

 greatly; the posterior end budded out a new structure of nearly 

 the normal shape for the posterior half of the body (Fig. 3, ^). 

 But this new part formed an angle with the anterior half, so that 

 the body of this individual was again crooked. At the same time the 

 anterior end extended a little. The two teeth remained near the 

 middle of the body, the larger one having been carried back a 

 little, so that it was a little behind the smaller one. 



Third generation. At the next division (forenoon. May 4) 

 the constriction appeared between the two tooth-like projections, 

 and the plane of division was oblique (Fig. 3, ^). Thus the 

 smaller one of the two projections was at the posterior end of the 



