DELSMAN: Fish Eggs and Larvae. 99 
several days or even weeks, I observed several kinds of eggs from the 
Java Sea already hatching at the end of the first day, not yet 24 hours old. 
In studying the fish eggs from the Java Sea it seems best to begin 
with those species which are the most common and most easily recognizable. 
And then our attention is, of course, drawn in the first place by those 
with a large diameter. Not only are these eggs the most obvious ones 
but they also offer the advantage that the larvae at the time of hatching 
are further developed than those from eggs with less yolk and thus present 
more characteristics from which the species may be recognized. On the 
other hand we have no guarantee whatever that the eggs thus chosen for 
our study belong to fishes. which are of economic value. In working out 
their development we even run the risk that the largest or most obvious 
kinds of eggs may prove to belong to little fishes only or to species of 
no economic importance whatever. 
This happens to be the case with the first number of the present 
series, the first of the eggs whose development | hope to trace and to 
describe here. It proved to belong to the flutemouth, Fistularia serrata, 
a fish which is related to and resembles much the well-known sea-needles. 
Judging from the general occurrence of the eggs and larvae in my catches, 
it must be a very common fish in the Java Sea. Yet the fishermen hardly 
know it since it is hardly ever caught in their nets. The egg is conspicuous 
by reason of its rather large diameter, this being on an average 1600 u 
(1 observed 1500—1700 u). The yolk is clear and contains no oil-globule. 
A peculiarity which was of great help to me in recognizing this egg is the 
double egg-membrane, the two membranes being separated by a little dis- 
tance (fig. 1 and 2, a and 5). The outer one is the thicker and stronger. 
The development of the egg takes, for the Java Sea, a rather long 
time: it requires four days to hatch. To give a description of the succeeding 
stages | take as an example a catch made on December 21, 1920, 
North of Middle-Java, 109° 42’ E. 6° 30’ S. From this catch | isolated 23 
eggs of this kind. They were all in the same stage of development, showing 
a multicellular blastoderm. Evidently spawning had taken place in the 
morning or during the preceding night. The latter supposition seems to 
me the most probable one, since at another occasion I found eggs with 
a very young blastoderm at 7- a.m The eggs floated near the surface of 
the water with the blastoderm turned below. In the course of the day the 
blastoderm extended slowly on the surface of the yolk 
The next morning the rudiment of the embryo had become visible, 
though the yolk had not yet been grown round completely by the blasto- 
derm. The latter extended over about ?/,—%/, only of the surface of the 
egg. Soon after the “yolk blastopore” becomes pearshaped and in the 
course of the day it closes. The rudiment of the embryo now extends 
round half of the circumference of the egg (fig. 1). The segmentation of 
the mesoderm into somites becomes evident. No pigment is yet to be seen. 
