castle: embryology of ciona intestinalis. 205 



II. MATERIAL. LIFE HISTORY. 



The material for this study was collected in the months of August and 

 September of two successive seasons, 1893 and 189-i. Tlie species em- 

 ployed seems to be, beyond question, the Ciona intestinalis of Flemming, 

 a classical object of study on the other side of the Atlantic. It was made 

 the subject of an extensive monograph by Roule ('84) ; its larval histoiy 

 has been studied by Kowalevsky ('66 and '71) and by Willey ('93); its 

 cleavage stages by Samassa ('94); its fertilization stages by Boveri ('90); 

 and the formation of its egg envelopes by Fol ('84). Loeb ('91) also 

 has employed it in certain physiological investigations. The specimens 

 which I collected at Newport answer fully to Roule's detailed descrip- 

 tions of the species. The large size (8-10 cm. long) attained by individ- 

 uals at Newport under favorable conditions confirms Roule's conjecture 

 that the forms described from the United States as Ascidia ocellata by 

 Louis Agassiz, as A. tenella by Stirapson ('52), and as Ciona teuella by 

 Verrill ('71) were only small-sized individuals of Ciona intestinalis. 



Specimens were obtained by me from two different localities just 

 within the entrance of Narragansett Bay. The animals were usually 

 found adhering to the under side of stones at a depth of from a few 

 inches to a few feet below low-water mark. Upon removal to the labora- 

 tory they were carefully washed and placed in aquaria whose water was 

 kept fresh by a jet of air. Once a day the water was changed, and the 

 aquaria thoroughly cleaned, to prevent the accumulation of bacteria or 

 other possibly injurious organisms. This painstaking treatment was 

 probably lumecessary, for the animals are very hardy and bear ill-treat- 

 ment well. For example, I have kept specimens for weeks at a time in 

 small glass aquaria without change of water, and the only signs of mis- 

 use which they exhibited were a slight shrinkage in size and a greatly 

 diminished production of eggs, — both symptoms referable to an insuffi- 

 cient food supply. 



Ciona, like all other Tunicates, is hermaphroditic, and the number of 

 eggs produced by a single adult individual in the course of a season must 

 be enoi-mous. Often hundreds are deposited in a single night. Under 

 normal conditions each adult individual, during the summer months, 

 lays eggs once in every twenty-four hours, with the regularity of the 

 sunrise. 



Korschelt u. Heider ('93, p. 1267) state that in most cases among the 

 Ascidians self-fertilization appears to be prevented by tlie ripening of the 



