ARACHNIDA. 627 



of what often occurs among all degraded forms, of a recur- 

 rence to the archetypal form of the articulate type, and not for 

 this reason, as some authors have done, would we place the 

 Arachnids of Latreille in a class by themselves, below the 

 Myriapods ; nor on recurring to the spiders alone, with their 

 high organization and wonderful instincts, w^ould we follow 

 Professor Owen and others in placing them even above the 

 true insects. 



We must look upon the Spider as a hexapodous insect, de= 

 graded, wingless, and partially decoj^haUzed. A part of the 

 elements, constituting the head in insects, have been, as it 

 w^ere, withheld from the head and detained in the thorax, which 

 has thus an increase in one pair of limbs. On the other hand, 

 the sensorial, or pre-oral, region of the head, is wanting in two 

 most important members, i. e., the compound eyes and the an- 

 tennae. Both Zaddach and Claparc-de state that there are no 

 organs in the spiders homologous with the antennoe of insects. 

 The simple fact that the homology of the organs generally is 

 so close between the two groups shows that they must fall into 

 the same class. The same can be said of the Myriapods. 



The circulatory system is very perfect in the spiders and • 

 scorpions, but in most of the lower mites there is no dorsal 

 vessel, or vascular system at all, the fluids being supposed to 

 circulate in the general cavity of the body, "and by the aid 

 of the muscular movements and the contractions of the intesti- 

 nal canal, transferred in an irregular manner hither and thither 

 in the visceral cavity and in the extremities." (Siebold.) In 

 the Phalangidce there is a distinct, three-chambered dorsal 

 vessel, or heart. In the spiders and scorpions, however, the 

 vascular system is highly organized, as shown by Newport (in 

 the Scorpions), and Claparede (in Lycosa). Here then, is, as 

 in Sphinx, a dorsal and ventral vessel with lateral veins, or ve- 

 nous sinuses, performing the functions of true veins. The main 

 iorsal vessel is mostly situate in the abdomen, as the hings 

 have their seat in that region, where the most important respi- 

 ratory function, that of supplying the bk)0(l witli fresh oxygen, 

 is performed. Claparr-de has shown that in Lycosa the blood 

 flows through the dorsal vessel from the head, instead of towards 

 the head, as in the six-footed insects. 



