GAMETOGENBSIS OF SACCOCIRRUS 33 



some figures of centrifuged eggs of Chaetopterus and Nereis 

 which lead me to beHeve that in these animals the egg contains 

 fatty yolk (or oil) and nucleolar deutoplasm as in Saccocirrus. 

 In Chaetopterus he finds the layers in the centrifuged egg to 

 be a grey cap, upper (the ' fatty yolk ' of this paper), a clear 

 area in the middle, and a lower layer of ' yolk ' (my ' nucleolar 

 deutoplasm ' and mitochondria) ; these areas correspond 

 with the layers in the centrifuged Saccocirrus egg (p. 18). 



Now, speaking of these layers in developing embryos and of 

 formative stuffs in general, Lillie remarks : ' So far as they 

 (formative stuffs) are to be identified with the visible sub- 

 stances segregated by the centrifuge, it would appear to be 

 indicated by experiments that they can play no specific role 

 in differentiation, because in centrifuged eggs they may 

 occupy variable positions in the embryo.' This view coincides 

 with that of Morgan (quoted in my previous paper (17)) and 

 with Miss Beckwith's study on Hydractinia. Any physiological 

 derangement during the development of centrifuged eggs seems 

 to be due either to mechanical difficulties of massed yolk or 

 to absence of nutriment. 



It is interesting to note, too, that Morgan came to his 

 conclusion partly as a result of work on Echinoderm eggs, 

 where Schaxel finds an emission of ' chromatin ' granules. 



{g) The Probable Part played by Mitochondria 

 and Golgi Apparatus in Heredity. 

 Modern cytologists tend to become divided into two groups — 

 those working on the nucleus and those working on the cyto- 

 plasm. Nearly all modern text-books dealing with Heredity 

 and Sex treat exclusively of the part played by the chromo- 

 somes in the mechanism of Heredity, and most observers are 

 satisfied to accept the view that ultimately the nucleus is the 

 seat of the substances which contribute to bring about the 

 phenomena of Heredity. ' Die Mitochondrien sind die proto- 

 plasmische Vererbungssubstanz ' is a statement which serves 

 to show us that the chromosome theorist is not alone in this 

 field. In the germ-cell cycle the chromosomes have been 



NO. 261 D 



