206 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
male and female sexual elements at different periods; although in some 
cases, where the sexual products. mature simultaneously, self-fertilization 
is not excluded. Neither of these statements holds good for Ciona. 
Although in the adult period it produces both sexual elements through- 
out the spawning season, and discharges them simultaneously, self-fer- 
tilization rarely occurs, — a conclusion to which I have been led by 
repeated experiments. The most complete series of these experiments 
will be briefly described. 
The observation had been made that an individual accidentally left 
overnight in an aquarium by itself laid eggs which failed to develop; 
whereas, when two or more individuals were placed together in an aqua- 
rium, all other conditions being the same, the eggs laid developed almost. 
without exception. 
First Experiment. 
Acting on the suggestion thus offered, 1 placed together in an aquarium 
two or three small, clear individuals (evidently young) ; in another aqua- 
rium was placed an equal number of very large-sized (old) individuals. 
A greater number of eggs was laid by the large individuals, as one would 
naturally expect, but the eggs in both aquaria were perfectly fertile. 
This experiment showed that ripe eggs and sperm are produced both 
by young and by old individuals. 
Second Experiment. 
Twenty rather large-sized individuals were selected for experimentation 
and divided into two lots, A and D, of ten individuals each. The animals 
of each lot were carefully washed and placed in clean glass dishes filled 
with fresh sea-water. The individuals of lot A (Table L.) were placed 
each in a separate dish, those of lot B (Table IT.) were placed two in a 
dish. The next morning a careful examination of each aquarium was 
made to determine what proportion of the eggs laid had been fertilized. 
The experiment was repeated on five successivo days; on the sixth day, 
as a control experiment, the lots were interchanged, the animals of lot 
A (Table IL) being paired, and those of lot B (Table I.) isolated. The 
results for the six days are embodied in Tables I. and Il. 
Taking an average of tho fifty-eight cases in which eggs were laid by 
isolated individuals (Table I.), we find that 4.8% of the eggs wero fertilized. 
The occurrence on a single day in two cases of fertilization of 90% of the 
eggs laid makes me suspect that the dishes were not properly cleaned 
on that day, and that live spermatozoa may have remained clinging to 
the sides of the dish after the previous day's experiment. If so, and if 
