568 CLASS ix. 



(Telephonus} , or lying side by side form an abdominal cord with- 

 out ganglia, as in the spiders. A chain of ganglia, as in most 

 insects, is found in Tardigrada, in Pycnogonida 1 , and in Scorpio 

 alone. In the Pycnogonida, the four ganglia, forming the row, lie 

 close together, without connecting cords, just as SwAMMERDAM has 

 figured the nervous system in Pediculus (see above, p. 301). In 

 Scorpio, on the contrary, they lie, seven in number, at considerable 

 distances apart, and are connected by two strings 2 . Above, and 

 commonly close upon the thoracic ganglion, is placed a ganglion 

 which may be considered as cerebral ganglion; in very simply 

 organised arachnids it is seen as a simple commissure on the oeso- 

 phagus ; in others it is oblong and formed of two small parts, 

 mostly conical or pear-shaped, lying side by side. From it arise 

 the nerves of the mandibles and of the eyes. Between this cerebral 

 ganglion and the thoracic ganglion, there is always an opening, 

 mostly very narrow, for the passage of the oesophagus, which is 

 surrounded on each side by the nervous connexion of the two gan- 

 glia. That the first ganglion is smaller than the second, and not 

 broad, as in most insects, depends, without doubt, principally upon 

 the absence of the compound eyes, whose nerves, in insects, have 

 such a large development. Interesting also is the exceptional form 

 of the nervous system in Phalangium, where the nerves proceeding 

 from the thoracic ganglion form eight ganglia in their course, four on 

 each side, not behind one another in a row, but at different heights, 

 dispersed on each side of the body, and distant from each other 3 . 



Traces of a distinct nervous system for the intestines, of that 

 system which we indicated above, in insects, as answering to the 



1 QUATREFAGES Ann. des Sc. nat. 3ieme SeVie, iv. 1845. Zoologie, p. 77, PI. I. 

 and IT. 



2 TREVIRANUS Ueb. d. inn. Ban der Arachn. s. 14 16, Tab. i. fig. 13, and espe- 

 cially Zeitschr. fur PJiysiol. iv. 1831. s. 8997, Taf. vi. and the elaborate fig. of 

 NEWPORT Phil. Trans. 1843, Part i. PI. xn. That the nervous system in Phnjnus 

 and Telephonus is formed not after the type of the scorpions, but of the spiders, was 

 announced by me in the Tijdschr. von Nat. Gesch. en Physiol. ix. 1842, bl. 75> an( l * 

 1843, bl. 369, 370. In Telephonus, at least, it would be difficult to have anticipated 

 this, and it is also in contradiction to the rules, already contradicted indeed by other 

 instances, which STRAUS DURCKHEIM formerly laid down for the form of the nervous 

 system of articulate animals. Consid. yen. s. I'Anal. comp. des Ani. art. pp. 364, 3^5> 



371- 



3 TREVIRANUS Verm. Schr. i. s. 38, 39, Tab. iv. fig. 24, TULK 1. 1. p. 325, PI. v. 



