MATURATION OF OVUM IN ECHINUS E8CULKNTU8. 179 



living eg-g- has been Asterias. Notwithstanding this, 

 little is known as to the finer details of maturation. 

 Hartmann (1902) has, since this paper was written, pub- 

 lished an account of the changes in this egg up to the forma- 

 tion of the first polar spindle. The early observations were 

 made on the entire egg — either in the living state, or 

 fixed and cleared. The polar bodies in Echinus are 

 normally thrown off within the ovary, and when the naked 

 eggs are shed into the sea water they remain entangled 

 in the connective tissue of that organ. Sometimes it may 

 happen that a partially immature ovary may be manipu- 

 lated and some ova caught in the maturation stages. In 

 the starfish, on the other hand, the eggs commence to 

 show the phases when placed in sea water, and they can be 

 watched. Again, by shaking immature sea-urchin eggs 

 the stages can be induced artificially. Boveri (1890) has 

 figured a few stages after the formation of the first polar 

 spindle in Echinus micro tube rculatus, but either the 

 chromosomes, which are very minute in Echinus sphaera, 

 are still more minute in Echinus microtuberculatus, and 

 cannot be further analysed, or he has not seen the figures 

 which I have made out by my methods. Further, the 

 number of chromosomes is different. Matthews (1895) 

 examined maturation in Asterias Forbesii. He was able 

 to obtain only one ovary showing the stages up to the forma- 

 tion of the first polar spindle, but supplemented his observa- 

 tions by stages obtained by shaking the eggs. He describes 

 the behaviour of the centrosomes, but gives no details as to 

 the chromatin. Wilson, in his atlas of 'Fertilisation and 

 Karyokinesis,' shows a single photograph of a second polar 

 spindle in Toxopneustes, and Boveri has drawn a single 

 figure of the second polar spindle in his recent work pub- 

 lished in 1901. Haecker (1893) also gives a diagrammatic 

 drawing of the first polar spindle, but gives no description 

 of maturation. In none of these figures is the finer constitu- 

 tion of the chromatin elements represented. Cuenot and 

 other observers have written on oogenesis in Echinoderms, 



