78 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
At the time the shell is ready to be cast the tegumentary covering consists of 
(1) 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. 
The connective-tissue cells are now of large size and contain granules of glycogen. 
Claude Bernard first demonstrated the presence of glycogen below the carapace in 
Crustacea. Glycogen was extracted by Vitzou from the connective tissue, liver, 
lymph, and ovaries, during the molting period. Besides acting as a pancreas, the 
liver was found to be a great producer of glycogen during the molt. Glycogen is 
thus an organic reserve, which furnishes material for the growth of the new shell and 
tissues. According to Vitzou. Schmidt and Berthelot have shown that the chitin of 
the Crustacea contains a principle belonging to the same group as cellulose and lignin. 
This substance, under the influence of sulphuric acid, may be transformed into a body 
analogous to glucose. Hence the remark of Claude Bernard, that u without forcing 
the metaphor one may say that the Crustacea are enveloped in a carapace of wood.” 
(Legons sur les phenomenes de la vie, 1879, t. 2, p. 113. — 197.) 
The enamel is plainly the first product of the secretions of the skin which goes into 
the new shell, and when once laid down can not be competely removed except by a 
molt. The enamel is often partially removed by friction, as is seen in the abrasions 
on the shells of old lobsters or those about to molt. 
The surface of the shell, particularly that of the carapace, has a decided punctate 
appearance, due to the hair pores. These mark the points where setm either pene- 
trate the shell now or did so at an earlier stage of development. In the adult lobster 
the set;e of the carapace have disappeared or are worn down except upon its margins 
and in the orbital regions. In the fourth larva, however, the whole carapace is seen 
to be studded with hairs (fig. 113, 115, plate 35). 
If the carapace — better one without pigment — is examined with a hand lens, the 
surface is seen to have a beautiful though somewhat irregular mosaic appearance. 
It is divided into polygonal areas which inclose the hair pores. These markings are 
probably due, as Professor Patten has shown to be the case in Limulus, to shallow 
depressions in the enamel, dependent upon a peculiar bending together or clustering 
of the outer ends of the canaliculi. The hair pores open on the inner side of the 
shell in small blister-like elevations. 
A very minute pore of another character is scattered among the hair pores on the 
inner side of the shell. It has the appearai ice of a symmetrical crater with a minute 
tube issuing from it. This is the duct and opening of the tegumental gland. The 
distribution of these two kinds of pores would probably repay careful study. But 
few parts of the carapace, such as the white tendon marks (see p. 135), are wholly 
free from them. Toward the lateral margins of the carapace they become exceedingly 
small and numerous. Some of the superficial pits in the dorsal region, on the other 
hand, are very large. 
We thus see that the dense shell is 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 lie 
at the roots of the hairs, on the other. The bearing of these facts will be better appre- 
ciated when we discuss hereafter the function of the tegumental glands themselves. 
