Chapter X.— DEVELOPMENT. 
ANALYSIS OF THE COURSE OF DEVELOPMENT. 
The entire course of development for each individual may be conveniently divided 
into embryonic, larval, and adolescent periods, which close, respectively, with hatching, 
the emergence into the fourth stage, and the acquisition of the secondary sexual characters 
and full adult power, reached in the female, according to Hadley, at the twenty-third 
molt. The age of sexual maturity or the entire period from larva to adult is subject to 
great fluctuation, owing to individual variations, changes in the environment, and to 
other causes. A io-inch female lobster may be from 5 to 6 years old, or even older. 
There are really no sudden transitions, but only gradual progressive changes, the nature 
of which especially at the fourth stage is often disguised by the abrupt passage of the 
molt. 
The embryonic life within the egg membranes is the most constant, occupying 
approximately ten and one half months on the coast of Massachusetts, during which the 
stored yolk supplies the materials and energy for growth. When this period is closed 
at hatching, the egg membranes burst, and together with a larval cuticle are cast off, 
thus leaving the animal free to enter upon an independent career. A remnant of 
unabsorbed yolk always remains, however, in the mid-gut region and serves to tide the 
little lobster over a critical interval before it is thrown entirely upon its own resources. 
Pairing probably does not continue long after sexual union has been accomplished, 
yet when confined in ponds lobsters have been known to hold together for several weeks, 
and even to occupy the same shelter. (See p. 302.) 
Parental instinct developed in the mother is mainly directed to the safe fosterage 
of her eggs. The young disperse as soon as hatched, rising to the surface, where they 
swim as free pelagic organisms until their larval life is over. Development proceeds 
through a series of metamorphoses or individual changes, externally marked by a corre- 
sponding series of molts, in the course of which the old cuticle is periodically shed in its 
entirety and as one piece to give place to the new covering already formed. The abrupt 
molts thus furnish a ready means of following the development and growth of the crus- 
tacean step by step from infancy to old age. The embryo virtually molts several times, 
though its cast cuticle seems to be mostly absorbed. The first of these membranes to be 
shed and absorbed in the egg is secreted by the blastoderm, and was mistaken for a true 
yolk or egg membrane by the older observers. As we have already noticed, the ripe 
crustacean egg possesses but a single protective envelope, the chorion or flexible shell, 
which at hatching time has been reduced to a layer of great tenuity. 
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