NO. lO IF.KDINc; OKC.ANS OF AKAf HNIDA — SN0DC;RASS 3 



of conveying; liquids to the mouth from tlic i)rcy held and crushed 

 in tlie chchccrae. A comparative study (if the external arachnid 

 feeding organs shows, in fact, that the mouth parts are elaborations 

 of structures associated with the oral aperture to form a preoral 

 food recejitacle and conduit to the sucking pump. That such accessory 

 feeding organs are not j)rimitivc becomes evident when we fuid that 

 in each arachnid order a dillereni kind of structure has been evolved. 

 The several orders of the Arachnida. therefore, with resj)ect to the 

 feeding apparatus, have no >erial relation lo one another. 



The entomologist who takes uj) a study of Arachnida obviouslv 

 must readjust much of his anatomical outlook. Because insects and 

 spiders are closely associated in nature, the study of arachnids has 

 l)een a sort of sideline for entomologists; for which reason, jirobably. 

 we find in the language of arachnology various terms that havi- been 

 carried over from entomology, and, as might be exi)ected. often 

 api^lied to j^arts that have no homology with organs of insects. Par- 

 ticularly is this true with respect to the feeding organs. It is a part 

 of the object of the present paper to eliminate entomological terms 

 that have no proper application to arachnid anatomy. The vertebrate 

 zoologist, of course, might justly contend that entomologists have 

 no right to the many vertebrate terms that are given to insect struc- 

 tures. However, conceding that names may be legitimately borrowed, 

 they should be applied consistently at least within any one phylum ; 

 otherwise definitions become conglomerations, and morphology is 

 handicapped by a meaningless terminology. 



I. GENERAL DISCUSSION OF ARACHNID STRUCTURE 



The fundamental structure of an arachnid is best understood from 

 embryonic development. The young arachnid embryo (fig. i A, B). 

 as the embryos of other arthropods, consists of a segmented or 

 partly segmented body and a large head lobe ( HL ) , which may be 

 deeply cleft into lateral halves. Behind the cejihalic lobe are the 

 true somites, begiiming with the somite of the chelicerae (A. /). 

 which is followed by that of the pedipalps (//), and the four leg- 

 l)earing somites (III-VI). The embryonic head lobe of the arthropods 

 always bears the labrum, the eyes, and the antennae if the latter are 

 present, but the arachnids in common with the xiphosurids lack an- 

 tennae, though these appendages were well developed in the trilobites. 

 With development of the arachnid embryo, the labrum remains as a 

 preoral, or supraoral, lobe of the hea(J, but the ocular region extends 

 posteriorly on the dorsum (C, D, ///. ) and becomes the eye-bearing 



