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 1894. "The 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 history 
has been studied by Kowalevsky ('66 and '71) and by Willey (793); 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 Stimpson (752), and as Ciona tenella 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 unnecessary, for the animals are very hardy and bear ill-treat- 
ment well. For example, I have kept specimens for weoks 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 hermaphroditio, and the number of 
eggs produced by a single adult individual in the course of a season must 
be enormous, 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 the ripening of the 
