270 



FIELD. 



Fig. 51. Mature spermatozoon : Asterias Forbsii. Sea-water + dahlia, drawn 

 while it was living. Note the structure of the centrosome (c), also compare with 

 centrosome in Figs. 14, 22, 41, 42, 43, 49. 



Fig. 52. Mature spermatozoon of Arbacia pustulosa after one hour in chloride 

 of manganese 10% + dahlia. 



Fig. 53. Mature spermatozoon of Arbacia pustulosa, but after a drop of 

 methyl green, aqueous solution was run under the cover-glass. The nucleus has 

 burst and disappeared, leaving only the mitosome and tail visible. 



Fig. 54. The same result upon similar treatment of a spermatozoon of an 

 Asteroidea. 



Fig. 55. Spermatozoon, very nearly mature. Chaetaster longipes. Sea-water 

 + dahlia. 



Fig. 56. Spermatozoon of Asterias glacialis very soon after entering the cyto- 

 plasm of the ovum. Dahlia, methyl green, glycerine preparation. The mitosome 

 is left behind in the periphery of the cytoplasm of the ovum. 



Fig. 57. Spermatozoon of Asterias glacialis, later. Flemming, section in 

 paraffin. Safranin, section in paraffin. 



Fig. 58. Spermatozoon of Asterias glacialis. The male pronucleus ; the cen- 

 trosome now lies at the side of the nucleus of the spermatozoon. The radiations 

 are beginning to appear. The arrow shows the direction which the male pro- 

 nucleus is taking to meet the female pronucleus. The mitosome and tail have 

 been absorbed. Section in paraffin. 



