PROGRESS IN BIOLOGICAL INQUIRIES, 1939 89 
stationary screen. As originally designed, it provided insufficient 
screen area when the water level in the reservoir was low. The screen 
also had become damaged by ice. It was reconstructed and modified 
to correct the difficulties. 
ICHTHYOLOGICAL INVESTIGATIONS 
Fishes collected in the Panama Canal.—Complete lists of the fishes 
collected in the locks of the Panama Canal in 1935 and 1937, together 
with discussions of the intermingling in the Canal of fresh- and 
brackish-water species from the opposite slopes of the Canal Zone, 
and the extensive invasion of fresh or nearly fresh water by marine 
fishes, are included in a recently published paper by Dr. Samuel F. 
Hildebrand, entitled “The Panama Canal as a passageway for fishes, 
with lists and remarks on the fishes and invertebrates observed.” 
As indicated in the title, some invertebrates also are mentioned. 
Although many marine fishes enter and some pass through the locks, 
only one species, the tarpon, is known definitely to have completed 
the transit; in this case, from the Atlantic to the Pacific. Brackish- 
and fresh-water species from the opposite slopes intermingle freely. 
Fishes of Tortugas, Fla—A large monograph of the fishes of 
Tortugas, Fla., Jeft unfinished by the late Prof. William H. 
Longley, was completed by Dr. Hildebrand. A total of 435 species 
are listed, 29 of which were discovered during the investigation. 
Much information of taxonomic importance was gained, and the 
knowledge of the life histories of many species was oreatly ‘extended, 
especially of the shallow-water forms which could be observed in 
their natural environment by the use of a diving hood. 
American anchovies.—Taxonomic revisional studies of the Ameri- 
can anchovies were continued by Dr. Hildebrand. Many interesting 
relationships, unrecognized species, and ‘many misidentified speci- 
mens in various museum collections have been found. The numer- 
ous misidentified specimens in collections serve to show how im- 
perfectly the species hitherto have been known. 
Systematic studies —Isaac Ginsburg continued his systematic 
studies of American fishes. Accounts were prepared of the genera 
Enyphias, Barbulifer, Coryphopterus, and Parrelia, Material was 
gathered on the systematics of a number of other gobiid genera, 
with the object of preparing needed revisions. Population studies 
were made of some of the common species of Microgobius, 
Lepidogobius, and Bathygobius. 
Population studies strike at the very root of one of the funda- 
mental problems, not only of fishes, but of all biology, and that is 
the species problem. Offhand, this would hardly seem to be a prob- 
lem. The layman, especially if he is of the observant type, seems 
to be able to distinguish well enough the comparatively few species 
of animals and plants with which he is familiar. The specialist, 
however, if he is a careful worker, sooner or later is confronted with 
the following questions: What is a species? What is a subspecies? 
What is a race? This is a real and fundamental problem in biology, 
about which a considerable degree of misapprehension exists, even 
among systematists. In connection with the population studies an 
attempt was made to reach down below the surface of the problem, 
and to evolve general principles and a method that will contribute 
