INTERNAL STRUCTURE OF LOBSTER. 



193 



COMMON CRAB, ENLARGED. B, SINGLE 

 EGG GREATLY ENLARGED, SHOVING 

 MORE PLAINLY THE HARDENED THREAD 

 (t) BY WHICH THEY ARE ATTACHED TO 

 EACH OTHER. THIS EGG SHOWS THE 

 YOUNG CRAB JUST BEGINNING TO 



FORM. (After Morse.) 



a powerful swimming organ, but in the Crab it is useless as an organ of natation, being quite 



rudimentary, especially in the males, but in the females of all these Crustaceans it serves as the nest 



for the eggs (or " berries," as the fishermen call them). When 



first extruded by the female, these eggs are coated with a viscid 



secretion, which thickens into threads, and causes the eggs to 



adhere to each other and to the fine hairs with which the swirn- 



merets of the abdomen of the Lobster and of the female Crab are 



fringed, and, thus protected, they are carried about by the mother 



until hatched (Figs. 4, 5). 



If a longitudinal section (Fig. 6) were made through the hard 



and soft parts of a Lobster, it would be found that its nervous FJg 5 _ A? A FEW OF THE E(JGS QF THE 



system occupies the ventral, or belly surface, of the animal's body, 



and consists of two parallel chords, so closely united, that, save 



near the stomach, where they separate to form " the cesophageal 



ring," they present only the appearance of a simple chord having 



a single ganglionic enlargement at each segment of the thorax and 



abdomen. But where the gullet passes to the stomach, the most 



anterior thoracic ganglion sends forward two dis- 

 tinct chords, which are united by a commissure or 

 cross nerve behind the oesophagus, and have eacli 

 a small ganglion on either side which gives off 

 nerves to the mandibles, the stomach, the heart, 

 the liver, and the intestines. These chords then 

 unite once more in a single large ganglion in 

 front of the mouth, and hence called the supra- 

 oesophageal ganglion. This is the Lobster's brain, 

 and its nerves go to the feelers, the eyes, and the 

 other sensual organs of the animal. Above the 

 nervous system is the alimentary canal, or the 

 great duct or intestine by which the functions of 

 digestion and nutrition are carried on. 



We have already seen with what an array of 



weapons, claws, foot-jaws, jaws, and mandibles, for cutting, crushing, 



tearing, biting, and generally pulling to pieces, a Lobster's mouth is 



armed ; but, as if still further to insure perfect digestion, the stomach 



itself is provided with a set of calcareous teeth covered with strong 



ridges like the grinding surface of the tooth of a small Rodent or Kan- 

 garoo Rat. These gastric teeth (Fig. 7) triturate the food against a fixed 



calcareous ridge, also set in the wall of the stomach, and are moved by 



appropriate muscles. In the lower chamber of the stomach, leading to 



the intestine, and named the pylorus, a series of fine hairs are placed, 



which prevent the escape of the coarser particles of food, until they 



have been repeatedly subjected to the molar-like action of these gastric 



teeth. The liver in both the Crab and Lobster is a very large and 



highly complex organ, not solid like the human liver. The secreted 



fluid, or bile, is poured by two openings into the pylorus. Imme- 

 diately beneath the cephalic shield of the Lobster lie the heart and the 



great main artery which supplies the entire length of the body. The 



, f i , i -i In, stomach of Crab laid open ; b, b, b, fixed 



neart consists ot a single ventricle, which sives on six arteries by calcareous piate again?t which the two 



"-rtric teeth, q, a, are exposed; If/and 



6. DIAGRAMMATIC SECTION OF A LOBSTER'S BODY. 



a', the antennules : a, the antenna; r, the rostrum; h, the heart; ar, the 

 artery ; gl, the pills or branch!; c, the etnmach ; I, the liver ; g, genital 

 organs or ovaries; in, the intestine; an, anus; n, n, the nervous 

 pysti in with its Severn 1 ganglia or nerve masses; o, the optic ganglion : 

 c the cephalic ganglion; i, oasophageal ganglion. 



31, 



Fig. 7. GASTRIC TEETH OF 



LOBSTER AND CRAB. 



gastr 



&vthe 



which the arterial blood is conveyed to the various organs of the 

 body ; it also receives by two main trunks the blood which has 

 passed through the branchiae. The arteries have valves at their 

 openings, and after ramifying they end ultimately in capillaries, connected at last with what are called 



263 



