THE CRAYFISH 



227 



their habits on the ocean bottom, it is thought that they construct 

 burrows somewhat like the crayfish, in which they pass part of the 

 time. As they have the color of the bottom and as they pass much 

 of their time among the weed-covered rocks, they are able to catch 

 much living food, even active fishes falling prey to their formidable 

 pinchers. They move around freely at night, usually remaining 

 quiet during the day, especially when in shallow water. They eat 

 some dead food ; and thus, like the crayfish, they are scavengers. 

 Development. The female lobsters begin to lay eggs when 

 about seven inches in length. Lobsters of this size lay in the 

 neighborhood of five thousand eggs; this number is increased to 

 about ten thousand in lobsters of moderate size (ten inches in 

 length) ; in exceptionally large speci- 

 mens as many as one hundred thou- 

 sand eggs are sometimes laid. The 

 eggs are laid every alternate year, 

 usually during the months of July 

 and August. Eggs laid in July or 

 August, as shown by observations 

 made along the coast of Massa- 

 chusetts, hatch the following May 

 or June. The eggs are provided 

 with a large supply of yolk (food), 

 the development of the young ani- 

 mal 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 animals. 

 It is estimated that barely one in five thousand survives this 

 period of peril. At this time they grow rapidly, and in conse- 

 quence are obliged to shed their exoskeleton (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. 1 



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

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



Metamorphosis of a shrimp : a, nau- 

 plius or earliest stage ; b, c, d, later 

 larval stages ; e, adult. Note that 

 as the animal grows more append- 

 ages appear, and that these develop 

 backward from the anterior end. 



