VARIATION IN ECHINOID PLUTEI 
659 
Especial care was taken in getting the sea-urchins to the labo- 
ratory in the best possible condition. When brought in they were 
used at once. 
Each individual was washed in fresh w^ater, cut horizontally 
through the test, and the aboral portion, to which the gonads 
remain attached, placed upside down on a glass plate. In ripe 
individuals the eggs are at once extruded through the genital 
pores. Only individuals were used from which the eggs were ex- 
truded freely, individuals in which as MacBride has expressed 
it, ''this organ, ' ' i.e., the ovary, ''at a touch dissolved into eggs." 
The eggs were then transferred to sterilized sea water, washed 
once, and fertilized by the addition of sperm that had been obtained 
by the same method of extrusion and mixed with sterilized sea 
water. After the eggs had settled, the supernatant water was 
poured off and the eggs washed several times in sterilized sea 
water to get rid of unnecessary sperm. 
The percentage of fertilizations was high, practically every 
egg developing. When the swimming blastulae gathered at the 
surface of the water, between six and seven hours after fertiUza- 
tion, they were removed and transferred to finger-bowls filled 
with sterilized sea water, which were then loosely covered with 
glass plates. 
So far as possible absolute cleanliness was observed. The sea 
water that I have described as "sterilized" was obtained at high 
tide or at considerable distance from shore. It was brought in 
A simple solution of the matter was found during a visit to Tortugas in 1909, 
when I again worked with Toxopneustes. At Boca Grande, where the collecting 
was done, the sea-urchins were picked up by hand in water sufficiently shallow for 
wading. During the period of full moon, in two months, Toxopneustes was found 
in abundance, almost in masses, on parts of the bottom that were not covered with 
vegetation. Such individuals were found to have spawned, while the scattered 
specimens, obtained from the feeding grounds, gave reproductive elements in 
abundance. 
If we had been collecting here by means of a dredge, as at Beaufort, it seems 
probable that the greater number of individuals taken at this time would have 
been devoid of eggs. 
There is some evidence, then, that when these animals are ready to spawn they 
gather more or less closely together and that this movement is correlated with a 
definite time of month. 
