224 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



variations in the larvae and older stages. The normal coloration of the lobster has, 

 however, a protective significance. 



(47) Abnormal variations. — Normally the large claws are differentiated for either 

 catting or crushing the food, but a rare variation occurs in which the same type of claw 

 is developed on both sides of the body. The large crushing-claw may be either upon 

 the right or left side of the body, but this is a question of heredity, and it is probable 

 that all the young of a brood have the larger claw developed on the same side. 



(48) Repetition of parts. — The large chelipeds of the lobster are especially liable to 

 secondary outgrowths, which undergo a peculiar fission, giving rise to what appears at 

 first sight as a double claw. It is usually a double part rather than a double append- 

 age, although duplicate limbs occasionally occur. 



(49) Structure of ovary. — When the ovary is ripe it is of a dark-green color and 

 can be dimly seen through the membrane between the carapace and "tail." If the 

 wall of such an ovary is cut the eggs immediately flow out in a stream. The eggs if 

 immature invariably adhere together or to the substance of the ovary. 



(50) After ovulation the ovary is collapsed, of an opaque white color flecked with 

 green spots, ripe eggs which were left behind — or yellow spots, the remains of similar 

 eggs from the last reproductive period. The presence of degenerate eggs thus proves 

 that the animal has already become sexually mature and has previously laid eggs. 

 The ovaries of lobsters which have never before produced eggs have a uniform tint — 

 yellow, pink, gray, or green — and are unmistakable. (For histology of the organs, 

 see Chapter x.) 



(51) Development of ova. — The eggs are developed from mesodermic cells of the 

 ovarian stoma, and the massive food yolk is derived from three sources: (1) From the 

 protoplasm of the cells destined to become eggs; (2) from the degeneration of follicle 

 cells, and (3) from the ovarian glands. 



(52) When the lobster hatches, its reproductive organ is a minute cluster of 

 cells -£j mm. in diameter, and in the case of the female it takes from four to five years 

 for the organ to reach maturity. 



(53) The sperm cells are probably motile in the final stage of their history, but 

 nothing is known either as to how the spermatophores are conveyed to the seminal 

 receptacles or how the spermatozoa reach the eggs and fertilize them. 



(54) Young. — The lobster hatches from the egg as a pelagic free-swimming larva. 

 It lives at the surface of the ocean from six to eight weeks, when, after having molted 

 five or six times, it goes to the bottom and appears iu habit and general structure like 

 a very small adult animal. After reaching the bottom it travels toward the shore and 

 establishes itself in rock piles in harbors and at the mouths of rivers, where it remains 

 until driven out by ice. At very low tide they can be found by digging away the 

 loose stones. The smallest, from 1 to 3 inches long, go down deep among the loose 

 stones, where they are secure from every enemy. When they reach the length of 3J 

 to 4 inches they become bolder, leave their burrows in the rock piles, and seek the 

 shelter of stones, beneath which they excavate a shallow hole. Young lobsters are 

 also found in eelgrass and on sandy bottom in shallow water. 



(55) At the time of hatching, the egg membranes burst into two halves and are- 

 drawn off over the head. At about the same time the little lobster sheds its entire 

 cuticle; the plumose hairs which garnish its appendages are evaginated and, leaving its 

 mother, it swims up to the surface. The first larva has long rowing exopodites on its 

 thoracic appendages, and a six-jointed abdomen with spatulate telson. At the second 



