86 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



The interesting observations of Hyatt on the molting of a lobster were made at 

 Matinicus Island, Maine, July 21, 1880. The ecdysis was accomplished at 9.30 a. m., 

 and the lobster lived forty hours, when the shell had become but little hardened, being 

 still papery and pliable. In twenty-four hours after shedding the claws had swelled 

 out and assumed a transparent, watery aspect. An under tint of green was observed 

 in the shell. The crowns and points of the spines and teeth of the large claws had 

 become whitened. The ratio of increase in bulk was found to be 1.211; the ratio of 

 increase in breadth, 1.192; the ratio of increase in length, 1.010. This lobster came 

 out of its shell without splitting the carapace, and the "tail" was the last part to be 

 set free. 



Vitzou describes the molting of a lobster which he watched in the marine labora- 

 tory at Eoscoff on the 21st of July. He speaks of the membrane between the carapace 

 as being early ruptured, and points to this as a sign that the animal is about to molt, 

 but this can not be a normal occurrence. 



WITHDRAWAL OF THE LARGE CLAWS. 



The shell of the large claws is molted entire without a rupture in any part. This 

 means that the great mass of muscles which fills the terminal joints must undergo 

 distension and compression to an extraordinary degree. This will be better appre- 

 ciated by an examination of cuts 6 and 7, plate B. Out G represents the cast shell of 

 the left cheliped of the lobster (No. 7, table 24) which molted on July 13, and cut 7 

 cross-sections of the shell with their plotted areas, in the planes indicated in cut 6. 

 The flesh which fills the area la is drawn through the opening of the joint II (plotted 

 area shown in Ha), and later through III, the smallest part of the claw. The shell is 

 here distensible, however, owing to the absorption of lime from the upper surface, so 

 that probably in this part the area of the cross-section is increased until it equals that 

 of Ha. Finally the compressed and distorted limb is drawn through the quadrilateral 

 opening at the base IV (plotted area, IVa), as Salter says, much as a wire is drawn 

 through the contracting holes of a draw-plate. The latter is somewhat larger than 

 the opening of the subtermiual joint II. The area of the section of the largest part 

 of the claw (I, la) is more than four times that of the opening Ila, through which all 

 the tissues of the claw must pass. The muscles appear to be stretched out like a stick 

 of candy, but, apart from their elasticity, they are probably aided in accomplishing 

 this by the removal of water from the blood. The parts are very much distorted 

 immediately after they are free, and are quite hard, but they soon take up water and 

 assume their natural form, with a proportional increase in size. 



The areas of absorption in the three basal joints of the limb are easily distin- 

 guished, though less plainly circumscribed, in the hard-shell lobster. The shell of the 

 basal joint becomes a slender ring, which is not broken, as has been inferred, but 

 remains intact, as Salter (174) has already observed. 



In the crayfish, on the contrary, Reaumur (161) maintained that in molting the 

 shell of the " second and third" joints (meaning, as shown by his figure, the meros and 

 carpus — fourth and fifth joints) opens by a longitudinal fissure on the outer side. 



The two pieces are so perfectly adjusted to each other that they appear as one, hut at the time 

 of the molt, when the crayfish subjects them to strain, these tubes gape apart and thus permit the 

 passage of the extremity of the limb. 



After the molt the crack closes up and appears to be glued together again, as if 

 no rent had been made. This explanation of the withdrawal of the large claws is 



