DESICCATION IN PHILODINA ROSEOLA. 39! 



to say that drying is the cause. It is necessary to point out if 

 possible how desiccation causes the reproductive increase. 



In an earlier paragraph I have shown that the nuclear-cyto- 

 plasmic reorganization takes place in the ovary the same as in 

 other tissues, and that just subsequent to the addition of water 

 an increase in the number of ovarian nuclei takes place. I have 

 not been able to observe these elements in the act of multipli- 

 cation but I am sure concerning the results of the process if 

 not of the method. 



It seems, then, that we are dealing with an adaptive, structural 

 response of a special sort. Whereas in the other tissues the 

 reorganization of cell elements took place to satisfy a vegetative 

 or metabolic demand, here we have a similar reorganization, the 

 end of which is increased reproduction, and the stimulus to 

 which is in both cases, desiccation. 



In addition to the increase in the number of sexual elements, a 

 stimulus is also apparently given which leads to the immediate 

 development of some of these elements. 



That egg cells should be stimulated to develop as a result of 

 loss of water is neither a strange idea nor a new one. Loeb ('06) 

 in his experiments upon artificial parthenogenesis found that 

 the unfertilized eggs of Arbacia and Strongylocentrotus could be 

 induced to develop into swimming larvae by immersing them in 

 hypertonic sea-water and later placing them in water of normal 

 concentration. That the initiation of development was due to 

 the withdrawal of water he demonstrated by further experiments 

 in which the eggs were not put back into sea-water of normal 

 concentration. In this case only a loss but no taking up of the 

 water occurred, yet swimming larvae developed. 



Philodina is a parthenogenetic rotifer, and as has been shown 

 is stimulated to reproduce by removal of moisture from its 

 tissues and consequently from the sex cells. It would seem, 

 therefore, that we are here dealing with a process which is natural 

 and commonly employed by this parthenogenetic animal as a 

 result of environmental conditions but that the same stimulus 

 can be employed to bring about parthenogenetic development 

 among an entirely different group of animals which reproduce 

 normally by the sexual method. The steps in the two processes 



