162 SCIENCE PROGRESS. 



the persistent as well as bi-sexual nature of the spheres. 

 But on closer inspection of the facts it does not seem to me 

 that the evidence against persistence is really altogether of 

 a negative character. If the spheres have an altogether 

 mixed origin arising from either sex or being evolved de 

 novo in the egg, the appearances would be exactly those 

 which have been hitherto recorded. Consequently these 

 can be and have been used as positive evidence of a mixed 

 origin. Nor can there be any doubt that the attractive 

 speculations which sprang from the suggestive observation 

 made by Fol, and its startling confirmation in Guignard's 

 paper which followed close upon its heels, have exercised 

 an inevitable tendency in swaying the minds of observers 

 towards a confirmation of these views which are legitimate 

 only if the " Marche du quadrille " is the tune to which the 

 centrosomes invariably "dance" through the initial phases 

 of ontogeny. There are, however, other sources of evidence 

 bearing on these vexed questions, of which I shall treat 

 successively ; one involving our knowledge of the life-his- 

 tory of the spheres in successive generations of tissue-cells, 

 and another the as yet too scanty observations relating 

 to the same phenomena in several protozoan animals and 

 plants. 



J. E. S. Moore. 

 (To be continued.) 



