248 MANUAL OF ZOOLOGY. 



In the Lobster (fig. 95) the somites of the head and thorax 

 are amalgamated into a single mass, the " cephalothorax," 

 covered by a carapace or shield, which is developed from "the 

 lateral or epimeral elements of the fourth cephalic ring, which 

 meet along the back, and give way preparatory to the moult. 

 The tergal elements of the thoracic rings are not developed in 

 either Crabs or Lobsters ; when these rings are exposed by 

 lifting up the cephalothoracic shield, the epimeral parts alone 

 are seen, converging obliquely towards one another, but not 

 joined at their apices " (Owen). 



The first segment of the head bears the compound eyes, 

 which are supported upon long and movable eye-stalks or 

 peduncles. Behind these come two pairs or jointed tactile 

 organs, the larger called the "great antennae " (fig. 95,^2), the 

 smaller the " antennules " (a). The mouth is situated on the 

 under surface of the front of the head, and is provided from 

 before backwards with an upper lip (" labrum "), two " mandi- 

 bles," two pairs of "maxillae," three pairs of " maxillipedes " 

 or "foot-jaws/' and a bifid lower lip, or "metastoma." The 

 five remaining segments of the thorax carry the five pairs of 

 ambulatory legs, of which the first (fig. 95, i) constitute the 

 great claws, or "chelae;" the next two pairs (2 and 3) are also 

 chelate, though much smaller ; and the last two pairs are ter- 

 minated by simply pointed extremities. The segments of the 

 abdomen carry each a pair of natatory limbs, or " swimmerets." 

 the last pair being greatly expanded, and constituting, with the 

 " telson," a powerful caudal fin. Most posteriorly of all is the 

 post-anal plate, or "telson," which may be looked upon either 

 as an azygos appendage, or as a terminal segment which has 

 no lateral appendages. 



The mouth leads by a short oesophagus into a globose 

 stomach, in the cardiac portion of which is a calcareous appa- 

 ratus for titurating the food, which is commonly called the 

 " lady in the lobster." | The intestine is continued backwards 

 from the stomach without convolutions, and the anal aperture 

 is situated just in front of the telson. There is also a well- 

 developed liver, consisting of two lobes which open by separate 

 ducts into the intestine. 



The heart is situated dorsally, and consists of a single poly- 

 gonal contractile sac, which opens by valvular apertures into 

 a surrounding venous sinus, inappropriately called the " peri- 

 cardium." The heart is filled with oxygenated blood derived 

 from the gills, and propels the aerated blood through every 

 part of the body. The gills (fig. 83, 3,^) are pyramidal bodies 

 attached to the bases of the legs, and protected by the sides of 



