GERM CELLS IN PEDICELLIXA AMERICANA 3 



matic and germ-cells. The complete cycle of chromatic changes, 

 from one generation to the succeeding one, may therefore be 

 traced. 



Under such conditions as these, it was my hope that Pedicel- 

 Una would be a favorable object for the further study of the 

 problem proposed by Hacker, viz., the fate of the maternal and 

 paternal chromatin elements in the offspring. This, however, 

 proved not to be the case, though some suggestive conditions 

 have been observed. My principal study has, therefore, been 

 devoted to the history of the chromatin of the germ-cells. 

 These show remarkable similarity in their development in the 

 two sexes, and give results corroborative of those of Mont- 

 gomery and Sutton. Finally, the processes of fertilization and 

 early cleavage are described ; attention is drawn to the character 

 of the nucleolus, and to the individuality of the chromosomes 

 throughout the whole course of development. 



It gives me much pleasure to express my obligations to the 

 staff of the Department of Zoology in Columbia University, to 

 whom I owe my appointment as the John D. Jones Scholar at 

 the Cold Spring Harbor Laboratory ; but above all to Professor 

 E. B. Wilson, to whom my sincerest thanks are due. From 

 the very beginning he has spared neither time nor effort in his 

 guidance of the research ; and to him also do I owe a careful 

 revision of my manuscript both in word and in substance. 



I. Material and Methods. 



The material for this study was obtained at Cold Spring Har- 

 bor, Long Island, where Pedicellina occurs at several places in 

 the harbor. Thanks to the kindly interest of Professor C. B. 

 Davenport, the Director of the laboratory, a most favorable 

 spot was located where the colonies could be obtained in great 

 abundance. This was in an oyster-bed, lying in a shallow 

 channel separating the inner from the outer harbor, where the 

 material could be collected at low tide, in any quantity, by 

 removal from the oyster-shells which the colonies encrusted. 

 The breeding season is a fairly long one ; beginning about the 



