92 George Lefevre 



there shown that the eggs of this worm can be induced to develop 

 into actively swimming trochophores, in the absence of sperm, by 

 exposure for a few minutes to dilute solutions of acids, both 

 inorganic and organic. Nitric, hydrochloric, sulphuric, carbonic, 

 acetic and oxalic acids were used successfully, and in favorable 

 experiments from 50 to 60 per cent of the eggs thus treated de- 

 veloped into swimming larvae that could scarcely be distinguished 

 from normal trochophores of a corresponding stage. Continued 

 and more detailed examination of the material has yielded many 

 points of interest which are described at greater length in the 

 present paper. 



The experimental part of the work and the observations on the 

 living material were made at the laboratory of the U. S. Bureau 

 of Fisheries, at Beaufort, N. C, during the summer of 1904, while 

 the cytological study was completed in the following summer at 

 the Marine Biological Laboratory at Woods Hole, Mass.^ 



The development and life history of Thalassema mellita were 

 first described by Conn ('84, '86), but as most of his observations 

 were made upon the living material alone, his account is superfi- 

 cial and inadequate, and, as has been recently shown by Torrey, 

 many of his descriptions are radically wrong. A careful study, 

 however, of the maturation and fertilization of this worm has been 

 made by Griffin ('96, '99), while the early embryology has been 

 very accurately described by Torrey ('02, '03). With the ex- 

 ception of a brief communication by Kowalevsky ('72), and a note 

 by Cowles ('03) on the rearing of Thalassema trochophores into 

 the young worms, there exists no further literature on the develop- 

 ment of this genus. 



Hitherto, the egg of Thalassema has been known to develop 

 only after fertilization by sperm, but my work has shown that it 

 may readily be induced to develop parthenogenetically. It is, 

 moreover, a particularly favorable object for experimental work 

 of this kind. 



'I wish to express my thanks to the Hon. George M. Bowers, U. S. Commissioner of Fisheries, for 

 the privilege of occupying a table in the Beaufort Laboratory, and to Dr. Caswell Grave, Director of 

 the Laboratory, for many courtesies extended to me. My thanks are also due the Carnegie Institu- 

 tion for the grant of a table in the Marine Biological Laboratory at Woods Hole in 1905. 



