522 
ZOOLOGY: A. a MAYER 
assertive mating in Chromodoris. If the population is composed of a 
mixture of pure lines, then one effect of this type of copulation may 
well be, as in Paramecium (Jennings), the prevention of interlinear 
crossing. Certain generally accepted ideas regarding the life history 
of nudibranchs may tend to favor this view. The evidence for the 
presence of pure lines in the Chromodoris stock is, however, entirely 
inferential. It would, indeed, be almost impossible to obtain good 
evidence upon this point, unless, possibly, through a study of the rate 
of segmentation of the eggs; but the eggs of C. zebra are not well adapted 
for this work, and it is very doubtful if such evidence could be made 
conclusive. 
Another, and, I believe, at present better founded, suggestion con- 
cerning the effect of assortive mating is based upon the fact that the 
size of the egg-masses, and the number of eggs in each ribbon, as well, 
probably, as the number of egg masses deposited by each animal during 
a single season, increase directly with the size of the individual. On 
grounds of physiological economy — remembering that mutual fertili- 
zation is involved, and remembering also that each animal deposits a 
number of egg-masses at each spawning season — it may be argued that 
the mating of large individuals is an influence tending to increase the 
number of larvae beyond that which would result from random pairing. 
In some other nudibranchs assortive mating, if it occurs, may have a 
different, or an additional, significance. 
Summary. — Mating pairs of the nudibranch Chromodoris zebra are 
found to exhibit a rather high degree of correlation between the sizes 
of the two members. This is due to assortive mating, which may con- 
stitute an important influence tending to increase the numbers of 
larvae. 
1 Contributions from the Bermuda Biological Station for Research, No. 70. 
2 It was necessary to remove the animals from the water and place them, dorsal surface 
downward, upon a glass plate. 
CORAL REEFS OF TUTUILA, WITH REFERENCE TO THE MURRAY 
AGASSIZ SOLUTION THEORY 
. By Alfred Goldsborough Mayer 
DEPARTMENT OF MARINE BIOLOGY. CARNEGIE INSTITUTION OF WASHINGTON 
Communicated June, 22, 1917 
Tutuila, Samoa, is a purely volcanic island without elevated coral 
reefs or limestones. It is surrounded by a recent fringing reef which 
forms a mere veneer over the modern off-shore marine platform, and 
extends a short distance seaward, its precipitous outer edge being from 
