178 THOMAS H. BRTCE. 



In view of the hopelessly diverging resnlts for different 

 forms obtained by different observers^ an interest in the 

 behaviour of the chromatin during maturation has declined 

 of recent years, and the question of the centrosome has 

 occupied more attention. Results which came out led me to 

 certain conclusions, which, to my mind, tended to clear up in 

 some measure the confusion at present prevailing. As 

 the research was proceeding, Strasburger's work, ^Reduk- 

 tionstheilnng, Spindelbildung, Centrosomen, und Cilien- 

 bilden in Pflanzenreich' (1900), came into my hands. In 

 that work conclusions in the matter of the reducing divisions 

 identical with my own, and foreshadowed in several 

 previous botanical memoirs, are brought, by new com- 

 parative investigations, to a focus, and are made a means 

 of harmonising the apparently contradictory results in the 

 case of plants. This obviously increased the importance of 

 my own results, and inspired me to follow out, in spite of the 

 large amount of labour involved, the whole series of 

 phenomena, in order to obtain as complete a demonstration 

 of the facts as possible. 



Maturation in Echinus esculentus, L. 



Previous Observations on Maturation in 

 Echinoderms. 



The Echinoderm ovum has been the classical material 

 for all observations on the living egg. The earliest 

 observations on the maturation of the sea-urchin egg 

 were made by Derbes in 1847. Agassiz, in 18G4, described 

 the polar bodies in both Toxopneustes and Asteracan- 

 thion. Between 1872 and 1882 Van Beneden examined 

 the phenomena in Asterias, Hertwig in Toxopneustus 

 lividus and Asteracanthion, Giard in Psammechinus, 

 Fol in Asterias glacialis, Greeff in Asterias rubens, 

 and Flemming in Spasrechinus brcvispinosus, Echinus 

 miliaris, and Toxopneustes. Since then the favourite 

 material for the examination of the phenomena in the 



