THE AMERICAN LOBSTER. 77 



slough off." The remarkable statement that "the abdominal legs are molted before 

 the thoracic ones " would imply that the hinder part of the body is first withdrawn 

 from the old shell, which is not true. 



The statement that the lobster "remains inactive for nearly or quite a week, until 

 the new crust becomes hard," can not be accepted without modification, since the soft 

 lobster is frequently caught in traps, and the newly molted lobster often displays 

 surprising agility, and besides it requires more than one week for the shell to become 

 hard. 



Brook (26), writing in 1SS7 on the reproduction of the lost parts of the lobster, 

 has some interesting notes on the growth of the European lobster which he kept and 

 observed in an aquarium for nearly a year and a half in one instance, during which 

 period the animal molted four times. The ecdysis usually occurred at night, and the 

 exuvium was buried. 



No one, strange to say, has ever examined the cast-off .shell and observed with 

 sufficient care the areas of absorption. This has resulted in much useless discussion 

 as to whether the carapace splits along the middle line when it is cast off. I shall 

 refer to this hereafter. 



We are now concerned with the adult animal only. The molting of the embryo 

 and larva will be considered in Chapter xn. 



THE STRUCTURE AND GROWTH OF THE SHELL. 



The phenomena of the molt are unintelligible without a knowledge of the struc- 

 ture of the skin or integument. The histology of the shell in the Crustacea has been 

 studied with varying degrees of success by a number of naturalists — by Carpenter (34), 

 Lavalle (116), Williamson (205), and Tullberg (191$). The most accurate statement is in 

 the paper by Vitzou (197), on which I shall mainly rely in giving the following account. 



The skin as a whole is composed of dermis and epidermis, and consists of the 

 various parts shown in the diagram (cut 5). The epidermis is made up of a single 

 layer of chitinogenous epithelial cells, and of the shell which they secrete; the dermis 

 is composed of connective tissue, blood vessels, nerves, pigment cells, and glands. 

 The shell consists of four layers, namely: (1) the thin outermost layer, which I shall 

 call the enamel layer, apparently structureless; (2) the pigment layer, composed of 

 parallel lamella?, traversed by caualiculi and filled with pigment and lime salts; (3) 

 the calcified layer, devoid of pigment but otherwise like the last, forming the greater 

 part of the carapace; (4) a noncalcified inner layer, composed of very thin lamella?. 



The chitinogenous epithelium corresponds to the Malpighian layer of the epi- 

 dermis of the vertebrate, while the layers of chitin represent its horny cuticle. 



The vertical caualiculi correspond, as Vitzou has shown, in certain decapods, 

 to the boundaries of the chitinogenous cells; but this is not the case in the lobster, 

 where they are close together and very numerous. 



During the molting period the cells of the chitinogenous epithelium undergo a 

 great change. They grow out, vertical to the surface, into very slender and exceedingly 

 long rods. (Compare Cut 11, and figs. 171, 173, plate 43.) The epithelium formed 

 over the surface of a budding limb is of the same character. The chitiuous layers of 

 the new shell are formed by discontinuous thickenings of what, according to Vitzou, 

 maybe regarded as the upper wall of the epithelial cell. Thus are formed parallel 

 lamellae of varying density, which fuse with those of adjoining cells and make a contin- 

 uous shelly crust. 



