PROGRESS IN BIOLOGICAL INQUIRIES, 1926 679 
On May 21 a piece of floating wood was found in the pond with many 
hundred closely arranged eggs adhering to the under surface. The movements 
of well-developed embryos could be seen through the shells. A sample of these 
ggs was taken to the laboratory and more closely examined. Hatching began 
in the afternoon and was still in progress on May 22. Almost all of the 
emerging fry, however, were weak and dying, and before night all that had 
hatched, as well as the unhatched eggs, were all dead in the jar of water in 
which they had been placed. Fortunately, the nesting habits of this fish made 
detailed observations possible. 
After the discovery of the first eggs on the floating wood, several boards, 
about 3 by 10 inches in size, were placed along the banks of the pond, about 
8 inches under the surface. It was thus easy to take up each board for 
examination and then replace it in the soft pond bank. These nest boards 
Were given numbers, and daily observations were made. During the season 
it was possible to examine 20 nests; and several other nests, out of reach on 
the under surface of the various pipe and platform supports, were indicated 
by the actions of guarding fish. The last eggs were observed on August 6. 
The following data was secured from observations on the 20 nests mentioned 
above: 
Time of first appearance of eggs to first eggs eyed, average four days. 
Time of first appearance of eggs to first eggs hatched, average six days. 
Time of first appearance of eggs to total eggs hatched, average nine days. 
The eg°s of the blackhead minnow thus required a period of six days (at 
the temperatures given for the pond) from the time of their first appearance 
to the time of hatching. The eggs were not, however, all placed upon a nest 
board at once, but sometimes in as many as four successive lots. It was 
found that the eggs eyed and hatched in the exact order of their appearance 
upon the nest boards. No attempt was made to see if all the eggs on a certain 
nest were from a single female. Two fish, however, were all that ever were 
seen near a nest at the same time. 
The habits of adult blackhead minnows were especially interesting. One 
or both of the parent fish were always seen near the nest board. Usually 
they kept immediately under the eggs and were very active, moving fins, tail, 
and body constantly. The male fish was the more aggressive, and when 
attempts were made to eatch various males with a dip net, they would swim 
under, over, and around it, but refused to be frightened away from the nest 
permanently. When two fish were present, the female kept quietly under the 
nest board, at the shore end, and always returned to her position. 
Thus, the protective instinct seems to be highly developed in these minrows 
For example, on May 28 two males were found fighting vigorously. The scene 
of action was close to the nest of the larger fish, which had been observed 
often enough to be recognized easily, and hostilities evidently began when 
the smaller male discovered the loss of his entire nest and went in search 
of it. This nest had been removed to another pond to see if the eggs would 
hatch without parental protection. The male on guard at nest D, however, 
resented the inquiring stranger and was quick to defend his own eggs. The 
two fighting males had a firm grip on each other’s jaws and were shaking 
their heads and bodies strongly. As they approached the surface of the pond 
both fish were scooped up with one dip of the net and examined. Both were 
male Pimephales promelas. The color was deep black, especially about the 
head, with two large bands of gold from the belly part way up the sides, and 
a third, smaller patch of gold near the belly side of the peduncle. Tubercles 
were prominent on the snout. Both of these fish were returned, uninjured, 
to the pond. 
On other occasions the guarding males would nibble at investigating fingers 
whenever a nest board was touched. They appeared to become more fearless 
as the hatching time approached. This display of aggressiveness seemed to be 
essential, as many times water beetles and water bugs, both adults and larve, 
were taken in the act of destroying the eggs on some nest board. In fact, 
when nests were transferred to other ponds where these beetles were abundant, 
it was necessary to protect them with fine wire screen. 
The growth of fingerlings also was noted with interest. A large sample of 
blackhead minnow fingerling was measured on August 17. As the spawning 
had been more or less continuous from May 21 to August 6, it was not sur- 
prising to find the fish varying in size from 8 to 40 millimeters. Most of the 
