IN THE PLASMODIA OF MYCETOZOA. 269 



obvious inference is, that in an aggregated plasm-mass there is 

 something in the nature of the plasm which causes it to alternately 

 dilate and contract ; and that owing to surfaces exposed to air 

 being drier and therefore firmer than parts in contact with water, 

 the force of the pulsations is expended on the streaming of the 

 more fluid and extended portions of the plasmodium, as being the 

 lines of least resistance. The time occupied by each alternate 

 flow, viz. about a minute and a half, farther suggests that the 

 controlling pulsations of the plasm-masses may possibly be the 

 result of a slow respiration ; this being consistent with the inter- 

 change of gases between plasm and its environment, which is one 

 feature of its constant chemical processes. That dilations and 

 contractions do occur in plasmodia is also rendered likely by the 

 fact that swarm -cells, by the fusion of which the plasmodia 

 originate, contain vacuoles or vesicles which alternately enlarge 

 and diminish, as if by reason of the gradual accumulation and 

 discharge of certain contents. It may not be without significance 

 that the contraction of these slowly pulsating vesicles in the 

 swarm-cells occupies about a minute ; because, allowing for altered 

 conditions, this may be regarded as approximating to the minute 

 and a half, or thereabouts, occupied by the alternate currents 

 in plasmodia. Moreover, similar vacuoles are found in the granu- 

 lar plasm of plasmodia, and occasionally also in the hyaloplasm ; 

 and although some of these vacuoles are more stable, others slowly 

 disappear and reappear, as in the swarm -cells. There must 

 obviously be physical results of the distensions and easements of 

 the plasm during these slow pulsations ; and these are probably 

 a partial explanation, at lea.st, of the pressure and suction by 

 which the streaming is produced. It is still more likely that the 

 visible pulsations are but indications of a respiratory function 

 inherent in the whole mass of the plasmodium ; but which only 

 finds full expression when circumstances favour the free circu- 

 lation of the reversible currents under conditions already described. 

 When the temperature falls too low, or the air becomes too dry 

 for these activities, the plasmodium, if not sutficiently mature 

 to form sporangia, passes into a resting stage, and remains in 

 a state of suspended animation, until warmer and damper times 

 return. In this condition, the dry plasmodium, or sclerotium, as 

 it is called, can be preserved for months, and then resuscitated 

 by the application of water. Describing the reviving process, 



