Organisms Consisting of One Cell ^^S 



Stent or, it is to the point to hear what Johnson has to say 

 touching the reality of the process as compared with the 

 develo})ment of a metazoan. "Tlie conception," he says, 

 "that the development of a new infusorian by the process 

 of fission is an ontogenetic development, comparable in some 

 respects to the development of a metazoon, has impressed 

 itself strongly upon me in the study of fission in Stentor/' ^"^ 

 The course of events in the multiplication and development 

 of the animal is so illuminating that I reproduce four of 

 Johnson's figures, figures 11, 12, IS and 14, and would urge 

 the reader unacquainted with the subject but wishing to 

 get at the kernel of the position here defended to consult 

 the original memoir, especially for the anatomy and ontogeny 

 of the organism. 



The main exterior body-parts to which attention should be 

 directed and which are indicated on the figures are: a. z., 

 aboral zone^ h. p., buccal pouchy cl., cilia^ c. v., contractile 

 vacuole, ejc. p., excretory pore of contractile vacuole, I, line of 

 division, l.b.s., left boundary stripe of ramifying zone, o, mouth, 

 p., peristomal band, r. z., ramifying zone, vel., velum. 



The processes of division and development are so intimately 

 associated as to be inseparable. "The first sign of fission," says 

 Johnson, "is the formation of a rift (the anlage of the new 

 aboral zone) in the pellicula and ectoplasm near to and almost 

 parallel with, the left boundary stripe of the ramifying zone." *^ 

 (figure 11 a. z.) By examining tlie figures the reader may 

 follow quite satisfactorily the main events. The first step in the 

 develojmient of some of the new parts should be specially noticed. 

 The aboral zone, for example, as indicated in the quotation, is 

 initiated as a rift through the ectoplasm running down the side 

 of the animal's body, hence having no connection whatever with 

 the original aboral zone. A point of special interest in this 

 fact is that the organ in question for the new individual does 

 not arise from the same organ of the old, or parent individual, 

 either by division or budding. And this de novo mode of origin 

 is that followed by a whole series of organs and tissues ; the cilia 

 and membranellae of the aboral zone; the mouthy velum, and 

 pharynx; the frontal field; the ramifying zone; and tlie con- 



