PROGRESS IN BIOLOGICAL INQUIRIES, 1926 613 
In collecting young fishes we employ nets of various kinds. Silk plankton 
nets, small 1-foot nets at the surface, and the -meter and i1-meter varieties 
are used commonly for eggs: and larvae. The Petersen young-fish trawl, espe- 
cially designed for postlarval and larger fishes, is very effective. In order to 
determine the exact depth of distribution, closing nets are necessary, of course, 
but our work rarely needs such’ fine differentiation. It is highly desirable to 
exam ne the specimens immediately, for preservatives are apt to shrink and 
distort the material and to change the color. d 
Although the larvee of most fishes are totally unlike the adults, and at first 
glance offer no clue to their identification, there are a few characteristics that 
are permanent throughout all stages, from the embryo to the adult. Such a con- 
stant character is the number of vertebre and, later, the number of fin rays. 
In the earliest stages, before the fins are distinguishable, the vertebral count 
is practically the only means of identification. There are certain peculiarities . 
for such species, especially shape and pigment markings, which make them 
easily distinguishable subsequently, but the first identification is possible only 
by counting the vertebre. 
In some tiny specimens strong light will be sufficient to reveal the spinal 
column, but usually it is necessary to use stain, and in larger fishes to disect. 
Alizarin is used a great deal, as is new methylene blue. The fish is then 
cleared in clove oil, xylol, or oil of wintergreen, and mounted in balsam. 
These methods have been applied to certain specific problems. In relation 
to the cod problem, I have cooperated with Doctor Fish in the identification, 
description, and measurement of all eggs and larve, computing percentages and 
charting results. This work has not been confined to the cod, haddock, and pol- 
lock, but has included all other species taken with them. 
An unusual opportunity was afforded by the Arcturus oceonograph cal expe- 
dition for the study of larval fishes, their distribution over large areas in the 
Atlantic and Pacific Oceans, the embryology, food, and enemies, the determina- 
tion of unknown forms as well as new stages of known species, and the con- 
ditions of life under which they exist in the open sea. 
Throughout the cruise, larval and postlarval fishes were found distributed 
everywhere over the ocean, but the number of species and the actual abundance 
of specimens were strikingly different in the various regions investigated. 
From Bermuda, southward, in the Sargasso Sea area, every haul of the 
plankton nets and Petersen trawls yielded quantities of young fishes—often 
10 to 20 species at a time. Although this part of the Atlantic had been sub- 
jected to heavy storms for some weeks past, the larval fishes seemed to thrive 
well, if we can judge from the number of uninjured specimens taken. It would 
appear, also from the collections here in a region that typifies conditions of 
the open sea, that a great many ocean fishes spend the early part of their 
lives at the surface. Of 41 species that I recorded and described in late 
February and early March, approximately 80 per cent were found always at 
the surface, 10 per cent at depths of 100 to 200 meters, and 10 per cent only in 
nets from below 1,000 meters. 
The Pacific Ocean, in contrast with the Atlantic, although swarming with 
animal life, yielded noticeably few larval and postlarval fishes from March until 
the middle of June. Although every haul brought in a few larve, and the 
number of different species represented over the whole period was no less, 
the total number of specimens was much smaller than in the Atlantic during 
late February, March, and July. 
On the Arcturus I worked out the embryology and early development of 
five species of flying fishes, some of them taken from nests of Sargassum weed. 
The unusual modification of the fins was found to be evident even in the egg. 
The eggs of 15 different species, of which the development was previously 
unknown, were hatched in the laboratory. At the completion of the expedition 
I had figured and described 161 species of larval and postlarval fishes, and 
further study of the collections undoubtedly will reveal many more. I was 
fortunate in obtaining and hatching the eggs of the burrfish, of Corypheena, 
and even of Mola mola, the giant sunfish. Although this latter species may 
weigh almost a ton, as an adult, it starts life as an egg only 1 millimetter in 
diameter. ; 
The Albatross made an extensive collection of tropical larval fishes, and 
through my work on the Arcturus I hope to be able to identify many of these. 
A problem in which I have been interested since 1922 is the appearance and 
disappearance of tropical fish migrants at Woods Hole. The Gulf Stream, 
sweeping northward up our coast from the Gulf of Mexico, carries with it 
