782 NATURAL HISTORY OF AQUATIC ANIMALS. 



range higher in organization than those of the two latter, and the Lobster must, therefore, be 

 regarded as lower in the scale of being than our common Crab. 



The Lobsters find some of their nearest allies among the common fresh-water Cray-fish of our 

 rivers and small streams, with which they agree structurally in most particulars. The principal 

 differences existing between them, beyond size and shape, are sucb as would be readily overlooked 

 by the casual observer. One of the most important is as to the number of gills, of which there are 

 twenty perfect ones on each side in the Lobster and only seventeen to eighteen on each side in the 

 Cray fish. Some of the gills also differ in structure in the two groups. The other structural 

 differences need not be discussed here, nor do we propose to describe the anatomical peculiarities 

 of the Lobster in this connection, as they have been fully treated of in numerous scientific publica- 

 tions which are easily obtainable. It will suffice for our purpose to pass over in review the 

 principal external characteristics. 



The body of the Lobster, as may be readily observed, is made up of two general divisions, an 

 anterior one, called the carapax or cephalo-thorax, and covered by a single shell or shield above 

 and at the sides, and a posterior one, termed the abdomen, consisting of six segments and a 

 terminal flap, or telson. The dividing line between the head and thorax proper, which are both 

 contained within the carapax, is indicated on the upper surface of the carapax by a trans- 

 verse, curved groove. Underneath the thoracic portion of the carapax there are five transverse 

 segments, corresponding to the pairs of legs, of which the four posterior pairs are subequal in 

 size and much smaller than the anterior pair or claws. All of the legs are composed of 

 several and an equal number of joints; the two posterior ones terminate in simple points, while 

 the two in advance of them end in small claws. The anterior legs are very much enlarged, the 

 joints very unequal in size and very unlike in shape, the terminal joint, forming the claw proper, 

 being very greatly developed, hard and rugged, and very powerful. Each segment of the 

 abdomen or tail also has a pair of appendages on the lower side. In the female, the anterior five 

 pairs are small and slender, and constitute, the so-called swimmerets, to which the eggs are 

 attached after extrusion from the body and during incubation. The appendages of the posterior 

 abdominal segment are large, and each terminates in two broad plates which lie at each side of the 

 telson. In the male, the anterior pair of abdominal appendages are modified into the stiffened 

 styles, by means of which the sex may be easily distinguished. The functions of these different 

 appendages correspond with the same in the Cray-fish, which are described as follows by 

 Professor Huxley: 



" The Cray-fish swims by the help of its abdomen and the hinder pairs of abdominal limbs ; 

 walks by means of the four hinder pairs of thoracic limbs ; lays hold of anything to fix itself, or 

 to assist in climbing, by the two chelate anterior pairs of these limbs, which are also employed in 

 tearing the food seized by the forceps fbig claws] and conveying it to the mouth ; while it seizes 

 its prey and defends itself with the forceps." 



On the lower side of the body, in front of the claws, are several pairs of variously shaped 

 small organs, which surround the mouth and subserve mastication. Still farther in front are two 

 long feelers or anteniiie, and two smaller feelers or antenules, and also the two compound eyes, 

 situated at the ends of two short, movable stalks. The carapax terminates in front in a sharp, 

 >piny, and prominent projection or rostrum, which reaches out between the eyes. The gills are 

 siiii;it] on each side of the body, just inside of the carapax, in two cavities, called the branchial 

 chambers, which open behind, below, and in front, so that the water has free entrance. 



Three species of true Lobsters, constituting the genus Homarus, are now recognized by 

 naturalists. They live exclusively in the sea. The American species, Homarus americanus, in 



