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 lo-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, occup37ing 

 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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