388 CLASS ARACHNIDA, 



similar in form, but of various sizes, are composed of seven 

 articulations, the first two of which form the haunches, the 

 following the thigh, the fourth and fifth the leg, and the other 

 two the tarsus. The last is terminated by two hooks, usually 

 denticulated like a comb, and in many by an additional one, 

 but smaller, and without denticulations. The intestinal canal 

 is straight: it consists of a first stomach, composed of several 

 sacs, then towards the middle of the abdomen, a second 

 stomachal dilatation surrounded with silk. According to the 

 observations of M. Leon. Dufour (Annal. des Sc. Phys.tom.vi-), 

 it occupies the greater portion of the abdominal cavity, and is 

 immediately enveloped by the skin. It is of a pulpy con- 

 sistence, formed of small grains, whose peculiar excretory 

 ducts unite into many hepatic canals, pouring into the alimen- 

 tary tube the product of the secretion. At the middle of its 

 superior surface is a deep line, where the heart is lodged, and 

 which divides this organ into two equal lobes. Its form varies 

 like that of the abdomen, according to the species, thus its 

 contour is festooned in the Epeira sericea. In this sub- 

 genus, as well as in the Lycosa tarentula, its surface is 

 covered with a coat of a chalky white, cut into areolae, which 

 are easily perceived through the smooth skin of some species. 

 They are observed to obey the motion of the systole and dias- 

 tole of the heart. The individuals of both sexes often shoot 

 through the anus an excrementitious fluid, composed of one 

 part white as milk, and another black as ink. 



The nervous system is composed of a double cord, occupy- 

 ing the medial line of the body, and of ganglia, which distri- 

 bute nerves to the various organs. M. Dufour has been unable 

 to determine the number and disposition of these ganglia; 

 but, according to the figure which Treviranus has given of this 

 system, the number of ganglia should be but two. The obser- 

 vations of the latter also supjsly the deficiencies of M. Dufour, 

 relatively to the organ of circulation, which, according to him, 



