DAILY MIGRATION'S OF COPEPODS. 
119 
and the experiment was discontinued August 26. During all this period the males 
and females retained their characteristic distribution, and nothing whatever suggestive 
of daily migrations was observed. Thus the changes noticed by Groom and Loeb in 
barnacle larvae failed entirely to appear in Labidocene. 
Lights of different intensities were next tried. When an electric incandescent 
lamp of about 14-candle power was held at 10 centimeters from a glass vessel con- 
taining female Labidoeerse, the animals came to the side next the light; they like- 
wise went to the top or to the bottom of the vessel, depending upon whether the 
light was held above or below it. These same reactions obtained when a concentrated 
solution of alum was used as a means of excluding heat rays. The reactions are 
therefore due to light. 
When, in place of a 14-candle lamp, one of about 100-candle power was used, 
the results were very different. The Labidoeerae, on first being approached by the 
intense light, made one or two leaps and then swam directly away from the light. If 
the lamp was placed above them they moved to the bottom of the aquarium (about 30 
centimeters); if, now, the light was quickly brought under the vessel, the animals 
rose. This latter response was doubtless coupled with their negative geotropism. 
Thus it is obvious that female Labidoeerae are positively phototropic to light of low 
intensity, and negatively so to light of high intensity.* 
The phototropism of the males was not noticeably different in the intense light 
from what it was in the dim light. Under both conditions the} 7 were, as a rule, 
slightly negative. 
These observations make clear why the female Labidoeerae are not at the surface 
of the sea in the daytime. They are negatively phototropic to its bright light, and 
therefore pass downward to the deeper water, where, from absorption by the upper 
layers, the light has decreased in intensity. 
To demonstrate the validity of this conclusion, a jar of female Labidoeerae was 
covered with a glass dish containing 4 inches of a saturated alum solution to absorb 
heat rays and then exposed to direct sunlight about noon. Immediately on being 7 
put in the sunlight the animals retreated from the source of light and went to the 
bottom of the jar. In this respect they were like Simoc&phalus sinia as observed by 
Radi (1901, p. 83). On excluding sunlight from the jar the Labidoeerae again rose, 
and they could be thus driven up and down at will. 
The migrations thus produced undoubtedly imitated in miniature the natural 
daily migrations of female Labidoeerae in the sea. These animals migrate into deeper 
waters on the coming of daylight because of their negative phototropism to strong 
light. They return to the surface on the approach of night because of their positive 
phototropism for weak light and their negative geotropism, a combination which 
Loeb (1890, p. 42) has already shown in the larvae of the brown-tail moth. In this 
way the migrations of the females are accomplished, and the only reason why these 
animals do not carry out similar daily movements in the laboratory is because of the 
absence of one factor, intense light. 
♦ Conditions of this kind, so far as reactions to light intensities are concerned, were apparently first noticed by 
Famintzin (1867) in the protozoans C'hlamidomonas and Euglcna , and have since been observed in the following animals: 
Hydra (Wilson, 1891), Polygordius larva! (Loeb, 1893), Daphnia (Lubbock, 1884), and Lima x (Frandsen, 1901). 
