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BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
The proportion of close fertilized eggs was greater in this experiment 
than in the preceding. Many of the eggs so fertilized, however, never 
developed beyond the 2- or 4-cell stage. The cross fertilized eggs all 
developed normally and at the same rate. 
Combining the results of Tables III. and IIL a, and those of IV. and 
IV. a, we get an average of 7.7% of the eggs developing after close fer- 
tilization, and 95% developing after cross fertilization. These averages 
agree fairly well with those obtained from Experiment 2, which were 
4.8% and 94% respectively. 
Experiment 3 shows conclusively that, in the case of Ciona, eggs are 
to a large extent incapable of fertilization by sperm from the same indi- 
vidual as the eggs. Cross fertilization must, therefore, be the rule, and 
close fertilization the exception under natural conditions. The rare 
occurrence of close fertilization is probably due to a lack of mutual 
attraction between eggs and sperm produced by the same individual, an 
attraction invariably existing between the eggs of one individual and 
the sperm of another, and probably chemical in its nature. This case 
is paralleled in certain flowering plants, whose pollen will not germinate 
when placed on the stigma of the flower from which it was taken, though 
on the stigma of other flowers of the same species of plant it germinates 
readily. 
There seems to be a particular time of day in the case of each species 
of simple Ascidian for the discharge of the sexual products, Different 
aquaria, in which are placed individuals of the same species, if they are 
subjected to the same conditions of temperature, etc., invariably contain 
eggs in exactly the same stage of development. This shows conclusively 
that the time of egg-laying has been the same in the case of each 
aquarium. For, on account of the rapidity of development, a slight 
difference in the time of egg-laying would be readily detected by a dif- 
ference in the stage of development exhibited by the eggs in different 
aquaria. In the case of Ciona the sexual products are discharged about 
an hour or an hour and a half before sunrise. The stimulus to their 
discharge is probably the increasing light of daybreak. 
If at about the time mentioned one approaches the aquarium with a 
lighted lamp, he will see the animals suddenly contract violently two or 
three times in succession, then resume their accustomed tranquillity. A 
careful examination will then reveal the eggs floating as little golden 
specks in the thoroughly agitated water. Soon they begin to settle to 
the bottom of the aquarium and can then be collected in convenient 
quantities by means of a pipette. The violent expulsion of the contents 
