THE AMERICAN LOBSTER. 171 



THE FIRST STAGE. 



When the lobster has successfully escaped from the egg capsule, and shaken itself 

 free from its larval cuticle, it emerges as a free-swimming animal, rising to the surface, 

 where it remains until its pelagic life is over. A sketch of one of these young lobsters 

 is represented in plate 19, and a lateral view is given in plate 20. 



The animal is but little over a third of an inch long. The average length of 15 

 specimens was 7.84 mm., the extremes being"7.50 and S.03 mm. 



The body is segmented as in the adult 'form, the most striking characteristics 

 being the enormous compound eyes, the conspicuous rostral spine, the spatulate telson, 

 and the biramous swimming appendages, which, from their resemblance to the perma- 

 nent swimming organs of the Schizopods, have given to this and the two succeeding 

 forms the name of "Schizopod larvae." Functional appendages are wanting only in 

 the abdominal segments, where, however, very small buds of the adult swimmerets 

 can be seen beneath the cuticle, iu the second, third, fourth, and fifth abdominal 

 somites. 



The cuticle of the larval lobster is now as translucent as glass, and the organs of 

 the body — the heart and blood vessels, the alimentary tract, and rudimentary gills — 

 are seen with great clearness. The green food yolk has disappeared entirely, or is 

 reduced to a mere remnant, now more yellow than green, in the masticatory stomach. 

 Perhaps the most conspicuous internal organ is the yellowish-brown liver, or gastric 

 gland, the form of which on either side of the body, resembles a cluster of grapes. 



VARIATIONS IN COLOR. 



The color of the larval lobster is produced, as we have already seen, by a blue 

 pigment dissolved in the blood plasma and by chromatophores which lie in the dermal 

 layer of the skin, besides the pigment cells of the eyes. The distribution of the chro- 

 matophores is very characteristic aud it is to these that the brilliant colors of the 

 larvae are largely due. (See plate 19.) The pigment which they secrete is of two 

 kinds, bright vermilion and yellow. The red cells are the larger aud play the most 

 prominent role. The expansion and contraction of the chromatophores, by which the 

 animal becomes brightly colored or pale, ordinarily requires from ten to fifteen minutes 

 when stimulated by pressure. The chromatophores are distributed in the region of 

 the carapace, along its sides, aud in front of the cervical groove. When they are 

 contracted the animal is pale blue aud very translucent; when expanded the red cells 

 give it a very decided color. Larvre when struggling on the bottom to get free from 

 their old cuticle or wheu crippled iu any way are usually red, a commonly recognized 

 symptom of weakness. This, however, does not seem to bean infallible sign. Larvae 

 which were placed in a pool out of doors on a bright day in June became red in a 

 few hours while swimming at the surface in apparent vigor. (See p. 188.) 



Both the blue pigment of the blood and the yellow and red pigment of the 

 chromatophores are lipochromogens, which are converted into lipochronies under the 

 influence of alcohol and other reagents (see pp. 135-136). The stomach and liver are 

 sometimes bright red, which recalls an observation by MacMuun (132), A\ho concluded 

 from spectroscopic evidence that in the lobster (Homarxs f/ammarus) the euterochloro- 

 phyllof the liver might be carried to the hypodermis and converted into a lipochrome. 



