192 



NATURAL HISTORY. 



maxillipedes have branchiae attached to their bases. And now, in the succeeding five pairs of 

 appendages, a marked change occurs, for these are undoubtedly legs, not jaw-feet. They vary at their 

 extremities, the first three pairs being chelate, or clawed, at the end (Fig. 2, L), whilst the two last 

 pairs have simple extremities (M). The first pair (not drawn in our woodcut) are those enormously 

 large clawed nippers, so characteristic of the common Lobster, and which differ in form (like a dentist's 

 forceps), one being very heavy and blunt-toothed, and the other more slender, and having its pincer 

 more sharply serrated. The remaining four pairs of legs are of nearly equal size, and are true 

 walking limbs. The seven pairs of thoracic appendages carry the breathing organs (branchice) upon 

 their basal joints, or attached to the pleurce or side-walls of the thoracic somites (body-rings). There 

 are twenty of these structures on each side of the cephalothorax. They are pyramidal bodies, each 

 consisting of a central ascending stein with numerous delicate horizontal branches through which the 

 blood circulates. They are closely packed against the outside wall of each thoracic body-ring, and are 

 protected from all liability to external injury by the overarching sides of the great carapace or head- 

 shield. To aerate the blood thoroughly it is necessary that the water bathing 

 the branchiae should be incessantly renewed. This is brought about partly by 

 the very movements of the legs, to the first joint of which they are nearly 

 all attached, and partly by those long slender organs we have already noticed, 

 attached to the basal joints of the maxillipedes and also to the legs, called 

 epipodites, or upper footlets. These ascend between the gills, and serve not 

 only to keep them apart from each other, but they also impart a slight degree 

 of movement to them. The main agent, however, is the scaphoynathite, or 

 boat-like jaw, on each side (Fig. 2, H, sc\ which continually spoons out the 

 wa -ter from the gill-chamber in front, and thereby causes a fresh current to 

 enter from behind. 



The fourteen anterior segments which form the head and thorax in the 

 C ra k anc * Lobster being so constantly found blended together in one, are fre- 

 quently termed the cephalothorax, a very convenient name for this compound 



.-.,, i i i i < 11 /iiij.1 17 \ 



structure. Ihe seven. body-rings which loJIow (called the abdomen) are 



. . 



seldom so much altered that one cannot at once see the separate joints or 

 segments of which the body consists. In the Lobster, as seen by the woodcut 



(Fig. 1), all the seven rings can be readily examined separately, but in the Crab the abdomen is 



often quite small, almost rudimentary, and in one family (called the Leucosiadce) the joints are 



soldered together into one piece, forming a 



small hollow enamelled lid to protect the eggs. 



In Fig. 3 is seen the third ring of the abdomen 



of the common Lobster, which may serve to 



represent the main characteristics of the second , 



third, fourth, and fifth body-segments. Each 



of these has two paired appendages attached 



to the underside or sternum (s) springing from 



one " root-footlet " (p), and giving rise to two 



swimmerets, fringed with hairs, representing 



the inner (en) and outer footlet (ex). 



In the sixth body-ring these swimmerets 



are greatly broadened out, and the outer foot- 



let is divided into two by a transverse joint. 



m, , , .., ., ,, 



Ihese broad swimmerets, with the seventh or 



terminal somite (before spoken of as the 



" telson "), together form the expanded termination of the abdomen, which, by its forward projection. 



through the water, drives the animal backwards. But the appendages belonging to the first abdo- 



minal ring in the Lobster have their swimmerets modified, in the males, into a pair of grooved 



processes, each like a small bent marrow spoon, and in the female into flexible soft processes. 



The primary function of the abdomen in the Lobster, Prawn, and Shrimp, is undoubtedly that of 



Fig. 3. THE THIRD 



RING OF THE ABDOMEN' 

 OF THE LOBSTER. 



pieces) ;" p,r, ibcprotonoiiitff, 



or first foot-joints, each bear- 



ing ex an e.ropodite or outer, 



pddit" or?ol!r^simmeVTt r 



Fig. 4. SIDE VIEW OF COMMON CRAB WITH ITS ABDOMEN EXTENDED, 



AND CARRYING A MASS OF EGGS BENEATH. 6. THE EGGS. 



(After Morse ) 



