CRUSTACEANS 



221 



length) ; in exceptionally large specimens as many as one hundred 

 thousand eggs are sometimes laid. The eggs are laid every alter- 

 nate year, usually during. the months of July and August. Eggs 

 laid in July or August, as shown by observations made along the 

 coast of Massachusetts, hatch the following May or June. The 

 eggs are provided with a large supply of- yolk (food), the develop- 

 ment of the young animal taking place at the expense of this food 

 material. After the young escape from the egg they are almost 

 transparent and little like the adult in form. During this period 

 of their lives the mortality is very- 

 great, as they are the prey of many 

 fish and other free-swimming ani- 

 mals. It is estimated that barely 

 one in five thousand survdves this 

 period of peril. At this time they 

 grow rapidly, and in consequence 

 are obliged to shed their exoskele- 

 ton (molt) frequently. During the 

 first six weeks of life, when they 

 swim freely at the surface of the 

 water, they molt from five to six 

 times.^ 



Molting. — During the first year 

 of its life the lobster molts from 

 fourteen to seventeen times. Dur- 

 ing this period it attains a length of from two to three 

 inches. Molting is accomplished in the following manner: The 

 carapace is raised up from the posterior side and the body then 

 withdrawn through the opening between it and the abdomen. 

 The most wonderful part of the process is the withdrawal of the 

 flesh of the large claws through the very small openings which 

 connect the limbs with the body. The blood is first withdrawn 

 from the appendage ; this leaves the flesh in a flabby condition (a 



^ Recent economic investigations upon the care of the young developing lobster 

 show that animals protected during the first few months of free existence have 

 a far better chance of becoming adults than those left to grow up without protec- 

 tion. Later in life they sink to the bottom, and because of their protectively 

 colored shell and the habit of hiding under rocks and in burrows, they are com- 

 paratively safe from the attack of eneroies. 



Metamorphosis of a shrimp; a, naupliiis 

 or earliest stage; h, c, d, later larval 

 stages; e, adult. Note that as the 

 animal grows more appendages ap- 

 pear, and that these develop backward 

 from the anterior end. 



