nion or fusion of the
'anlagen' of the two eyes. Cases were observed which showed various
degrees in this fusion; it appeared as though the optic vessels were
formed too far forward and ventral, so that their antero-ventro-median
surfaces fused. This produces one large optic cup, which in all cases
gives more or less evidence of its double nature." (Stockard, "Archiv f.
Entwickelungsmechanik", Vol. 23, page 249, 1907.)

We have confined ourselves to a discussion of rather simple effects of
the change in the constitution of the sea-water upon development. It
is a priori obvious, however, that an unlimited number of pathological
variations might be produced by a variation in the concentration and
constitution of the sea-water, and experience confirms this statement.
As an example we may mention the abnormalities observed by Herbst in the
development of sea-urchins through the addition of lithium to sea-water.
It is, however, as yet impossible to connect in a rational way the
effects produced in this and similar cases with the cause which produced
them; and it is also impossible to define in a simple way the character
of the change produced.

III. THE INFLUENCE OF TEMPERATURE.

(a) THE INFLUENCE OF TEMPERATURE UPON THE DENSITY OF PELAGIC ORGANISMS
AND THE DURATION OF LIFE.

It has often been noticed by explorers who have had a chance to compare
the faunas in different climates that in polar seas such species as
thrive at all in those regions occur, as a rule, in much greater density
than they do in the moderate or warmer regions of the ocean. This refers
to those members of the fauna which live at or near the surface, since
they alone lend themselves to a statistical comparison. In his account
of the Valdivia expedition, Chun (Chun, "Aus den Tiefen des Weltmeeres",
page 225, Jena, 1903.) calls especial attention to this quantitative
difference in the surface fauna and flora of different regions. "In the
icy water of the Antarctic, the temperature of which is below 0 deg C.,
we find an astonishingly rich animal and plant life. The same condition
with which we are familiar in the Arctic seas is repeated here, namely,
that the quantity of plankton material exceeds that of the temperate and
warm seas." And again, in regard to the pelagic fauna in the region of
the Kerguelen Islands, he states: "The ocean is alive with transparent
jelly fish, Ctenophores (Bolina and Callianira) and of Siphonophore
colonies of the genus Agal