752 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



The second chapter deals with the phenomena of cncystation. Tliis 

 may, in a general way, bo said to bo provoked by moditications of the 

 medium which become unsnitablo for the life of the individual. Tho 

 author is of opinion tliat desiccation, or the evaporation of water, which 

 is so often invoked as the solo cause of cncystation, has not the imjiort- 

 ance which has been attached to it, for the modifications which are duo 

 to iiutrefaction play an equal if not a greater part than those due to 

 evaporation. The secretion of tho membranes of tho envelope of tho 

 cyst takes place from within outwards, and the density of the membranes 

 diminishes in the same order. Preservation-cysts must be distinguislied 

 frt)m division-cysts ; the membrane of tho former is quite membranous, 

 while that of the latter is more or less mucous, and soluble in potash, 

 or even in water. The membrane of the cyst is permeable to liquids, 

 but has the property of opposing the passage of certaiu bodies, or, in 

 other words, acts like a dead dialysing membrane. Active life persists 

 in the cyst until the complete elimination of the food-material which it 

 contains. The residue may be rejected between the body and the 

 membrane, or remain in the interior of the protoplasm under the form of 

 refractive masses. The contents of the cyst are rich in reserve-material 

 (glycogen) which gradually diminishes in cysts preserved in water. 



Appendicular organs such as cilia, cirri, or hooks are completely 

 absorbed at the time when the latest life-stage is complete ; the nucleus 

 preserves its normal form, and, if it is composed of several granules, these 

 only fuse with one another in the preservation-cysts. Cysts which are 

 preserved in air become highly refractive, and, after a diminution in 

 their volume resulting from the loss of water, they preserve the same 

 volume for an indefinite time. Cysts, on the other hand, which are 

 preserved in water, die after a more or less long time. 



Revivescence is variable, and is often effected by simple aeration or 

 under the influence of repeated movements of the support on which the 

 cyst is fixed. This is due to the permeable membrane of the cyst allowing 

 the passage of soluble matters which are favourable to the life of tho 

 infusorian. The mechanism of revivescence appears to be an absorption 

 of water considerable enough to swell the protoplasm and dilate the 

 membrane. Some Infusoria have no power of secreting a membranous 

 envelope. Bodies that produce an ansesthetic eftect on animals that have 

 a nervous system appear, doubtless on account of the rapidity of the 

 osmotic changes, to have a mortal influence on Infusoria. In one case 

 only — that of Nassula ornata — was a real anfesthetic influence only ; in 

 this species there is a grey spot which is constantly found in the left 

 anterior region, and is, possibly, a sort of localization of the nervous 

 element ; this spot takes on a deep brown colour with osmic acid. 



The observations wliich M. Fabre-Domergue has made on the pliysio- 

 logy of nutrition lead him to think that the digestion of food is eflected 

 by the same chemical process in all the forms examined ; they absorb 

 food presented to them in larger quantities than they can consume, for 

 they reject part without utilizing it. In perfect conditions of nutrition 

 (looked at in the largest way) reserve-material is stored up which is used 

 when the conditions become unfavourable to life. 



Conjugation of Vorticellidae.* — M. E. ]\Iaupas states that he has 

 been able to make complete observations on Vorticella nionilata, almost 



* Comptc-3 Rendus, cvi. (1888) pp. 1G07-10. 



