NATURAIv history OF AMERICAN LOBSTER. 
331 
Color of the larva . — The gay coloring of the larval lobster, aside from that con- 
tributed by the internal organs and contents of the ailmentary tract, is produced by 
a blue pigment dissolved in the blood plasma and by red and yellow chromatophores 
which lie in the dermal layer of the skin, besides the pigment cells of the eyes. The 
distribution and grouping of the red chromatophores is very characteristic, and it is to 
these that the brilliant colors of the larvae are largely due. The red cells are the larger 
and play the most prominent role. The expansion and contraction of the chromato- 
phores, by which the animal becomes brightly colored or pale, ordinarily requires from 
10 to 15 minutes when stimulated by pressure and released (fig. 35 and 36). The 
chromatophores are distributed in a number of well-defined regions, namely the cara- 
pace, in front of the cervical groove, the gill covers or sides of the carapace, the large 
claws and bases of the cephalo-thoracic appendages, and the dorsal surface of the abdomi- 
nal segments, including the telson. These centers of color distribution are well marked 
from a late embryonic period to the lobsterling or fourth stage, when the change in the 
lobster’s coloring is no less profound and abrupt than that of its structure and habits. 
When the chromatophores contract under the influence of a stimulus the animal becomes 
pale blue and very translucent; when they expand the vermilion cells give it a much 
more decided color. Pale blue at night, bright red by day is the rule, and among 
external agents sunlight seems to provide the main stimulus which causes the chromato- 
phores to expand, but other changes, like raising the temperature or applying pressure 
to the body, will produce a like result. If the young lobsters are suddenly placed in 
darkness they tend to become paler and if returned to the light to redden more or less 
promptly. But the internal conditions or physiological states of the animal evidently 
present another and highly variable factor. All larvae do not redden in the sun and all do 
not pale in darkness, while some respond more promptly to all such changes than others. 
When the larvae are seen struggling on the bottom of an aquarium, to get free from 
their old cuticle, when crippled in any way, or as Hadley remarks, when starved for 
some time, they so often turn red that this color has been regarded as a sign of weakness. 
On the other hand, if thousands of larvae hatched and reared indoors are suddenly set 
free in more brilliantly illuminated water outside, a large proportion of them will redden, 
though not all. It has been asserted that the young and adult in all stages are upon 
the whole more active by night than by day, and that the young tend to move toward 
the source of light, or toward the surface where they find their suspended food. If the 
latter statement were true, we should expect to find the young larvae at the surface of 
the ocean in the daytime and in active movement. Prof. S. I. Smith has taken the 
larvae in all stages in the surface waters of Vineyard Sound in the daytime, and in sev- 
eral instances when using an electric light at night. These larvae are often seen to pursue 
their prey by sight, and it has been shown that they can orient themselves through the 
medium of the eye. We thus seem to become entangled in a web of contradictory 
statements. The larvae are more active in twilight or at night, but seek the light, and 
pursue their prey in the daytime, by the aid of sight. Red is a symptom of weakness, 
but they redden in the light. 
