NATURAI^ HISTORY OF AMERICAN LOBSTER. 20I 



layer, transversed by vertical canaliculi, abounding in pigment and impregnated with 

 mineral salts; (3) the calcified layer proper, devoid of pigment, but otherwise like the 

 last, and forming the greater part of the shell substance; and (4) a noncalcified inner 

 stratum composed of very thin lamellae. 



The chitinogenous epithelium may be compared to the Malpighian layer of the 

 epidermis of the vertebrate, while the layers of chitin represent its horny cuticle, 

 though formed in a different manner. The vertical canaliculi of certain decapods, 

 according to Vitzou (272), correspond to the boundaries of the epidermic 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 undergoes a 

 great change, its cells being extended vertically into very long and slender rods (pi. xlvi, 

 fig. 2). The epithelium developed over the surface of a budding limb is of a similar 

 character. The chitinous layers of the new shell are formed by discontinuous thicken- 

 ings of what, according to Vitzou, may be 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 continuous shelly crust. 



At the time the shell is ready to be cast the tegumentary coverings consist of (i) 

 the old shell, (2) the new shell, (3) an intermediate structureless membrane, besides 

 the chitinogenous epithelium, and (4) the dermis. The new carapace, according to 

 Vitzou, is composed of the enamel and pigment layers only. The calcified layer is 

 not formed until after the molt. 



Certain peculiar cells which have been referred to as connective tissue become very 

 conspicuous at the molting period, particularly in the dermis, and experimental evidence 

 seems to show that they secrete glycogen which is used in the production of the new 

 shell, but no exact knowledge concerning these structures is available at present. The 

 enamel layer is the first formed, and when once laid down can not be removed except by 

 the shedding of the entire shell. However, it is worn away by abrasion, as seen in the 

 old hard-shelled animals, and its function is purely protective. 



The surface of the shell has a punctate appearance, due to hair-pores, which 

 mark the points where hairs or setae now pierce the shell or where they were present 

 at an earlier stage of development. In the adult lobster the setae of the carapace have 

 disappeared more or less completel)' except upon its margins and in the orbital region. 



The dense shell of this animal is in reality a veritable strainer, being perforated 

 by hundreds of thousands of minute passages, which lead from the surface to the parts 

 below it — to the tegumental glands on the one hand or to the sensory cells which he at 

 the roots of the hairs on the other. 



PERIODS, CONDITIONS, AND SIGNIFICANCE OF MOLTING. 



The hard-shell lobster is heaviest, has the firmest flesh, stands transportation best, 

 and is therefore most valuable for the market. A large percentage of all lobsters taken 

 during the fall and winter months are of this character, and nearly all lobsters caught 

 in March, April, and May belong also to this class. Shedders and soft-shell lobsters 

 are taken in greater or less abundance from June to October, varying somewhat with 



