34 ILLINOIS BIOLOGICAL MONOGRAPHS [244 



THE CYSTS 



Observations on cyst formation and development, like those on 

 movement have been confined chiefly to one species. In the Stenophori- 

 dae I have not been able to procure the dehiscence of any cysts ; in the 

 Gregarinidae observed, however, it was an easy matter to procure cysts 

 and watch their development. Cysts were taken from moistened fecal 

 masses or from the intestine by means of a needle and placed on slides. 

 Bits of broken glass were used to raise the cover slip, and distilled water 

 added. The cell was sealed with vaseline and placed in a petri dish well 

 vaselined along the edges. 



Cysts of the Stenophoridae observed were spherical or slightly ellip- 

 soidal. They are generally found in the posterior part of the intestine 

 and were not seen until fairly developed and rotation had ceased. It is 

 not difficult to determine in most cases that two individuals were in- 

 volved in making the cyst. The line of separation is often indicated in 

 the cyst and there is often a slight difference in density of the two 

 conjugants. In one instance one sporont was nearly black and the other 

 pale tan. This fact was not noted until after the cyst had been in the 

 damp chamber half an hour. In all cases observed the cysts became 

 lighter in color after being in the damp chamber a few hours. In freshly 

 opened intestines, cysts do not show a clear hyaline layer but after expo- 

 sure the extrusion of water causes the inner mass to shrivel and the epi- 

 eyst to swell so that the whole diameter is greater than at first. Al- 

 though cysts were kept in the damp chamber nine days no spores de- 

 veloped. Whenever still intact, the cysts were crushed at the end of that 

 time but there was no apparent differentiation of the protoplasm and 

 none was revealed by staining. Most of the cysts were, however, shriv- 

 eled and disintegrated. 



Cyst Formation in the Gregarinidae Leidyana erratica 



This species is in its normal sporont stage non-associative. The 

 young sporonts which have but recently lost their epimerites are nearly 

 transparent but as age advances density increases, due to the absorption 

 of food. The oldest sporonts are very dense and practically black in 

 the deutomerite so that the nucleus is not visible when they are alive. 

 The body in the young sporonts is long and rather slender, but it widens 

 appreciably in the older ones. Middle-aged animals are very active in 

 their movements but older ones are sluggish and tend to lie motionless 

 in masses (Fig. 230). 



In dense, sluggish individuals, one may expect cyst formation to 

 take place. The sporont retains its power to bend and twist after it has 

 apparently ceased to use its progressive powers. Sluggish individuals 



