og^ Louise Hoyt Gregory 



the nucleus, or at the extreme edge. In a few cases it seemed to 

 have disappeared at one region and the nuclear substance mingled 

 with the cytoplasmic material. 



While the micronuclei divide by mitosis, this division is inde- 

 pendent of cell division. During the latter process, four micro- 

 nuclei may pass directly into one daughter cell, and five to the 

 other, or six into one and seven into the other. All of the bodies 

 are of the same character as those described in the normal forms, 

 having a homogeneous central mass, surrounded by a clear area, 

 the whole body being bounded by a thin but definite membrane. 



After the planes have cut through, and the four young cells are 

 separated, rotation takes place individually within the membrane, 

 until the normal form is assumed. Usually the young individuals 

 overlap, as the space is not large enough for all four to be on the 

 same plane. As they increase in size, the membrane is broken, 

 and they escape from the cyst fully formed, with the posterior lobe, 

 mouth, contractile vacuole — all organs in position, but of one- 

 quarter the normal size. 



The formation of sporulation cysts is not common among the 

 Infusoria. Reproduction takes place, in general, by the simple 

 transverse division of the body, either within or without a cyst 

 membrane. One of the few examples of the formation of sporu- 

 lation cysts has been described by Rhumbler in the history of 

 Colpoda cucuUus. The food vacuoles are first eliminated, and 

 then a thin membrane or velum is secreted slowly on the outside 

 of the cell membrane. A space is left between the two membranes 

 into which the contractile vacuole discharges its contents. There 

 is no opening in the membrane, and the cell floats in its own cavity. 

 The body gradually loses its normal form, shrinks to one-half the 

 original size, and assumes a spherical shape. The cilia are lost, 

 the nucleus is invisible, all assimilation particles are eliminated, 

 and finally there is nothing left save a homogeneous mass of pro- 

 toplasm which ulitmately divides to form eight, ten, or twenty 

 spores. Evarts, in 1873, described a somewhat similar process 

 in Vorticella. 



Under certain conditions, such as a changed environment, un- 

 usual heat or cold, or because of some internal stimulus, perma- 



