246 KINGS LEY. . [Vol. VIII. 



Again, as I previously argued, the existence of similarly 

 placed tubules in certain Amphipods can be advanced as an 

 aro-ument for the closer association of the Arachnids and the 

 Crustacea. Still exact knowledge of these tubules in the Am- 

 phipoda is lacking. Nebeski ('80) regards them as diverticula 

 of the hind-gut, while Spencer ('85), upon histological grounds, 

 regards them as outgrowths of the mcsenteron and hence, like 

 those of the Arachnids, entodermal. It must be said, however, 

 that this evidence is not conclusive, as the limits of the hind- 

 gut are not clearly ascertained, and the assumption that these 

 are entodermal is based upon the absence of a chitinous cuticule 

 (Spencer, '85, PI. XIII, Fig. 2) and by a break in the character 

 of the epithelium in the alimentary canal at the point of origin 

 of these tubes, the tubes themselves apparently belonging to 

 the anterior portion. 



All, then, that can be argued from the various structures 

 known as Malpighian tubules is that homoplastic and analogous 

 organs, rather than exact homologues, are included under this 

 name ; that their existence in both Arachnids and Hexapods 

 is an argument against the close association of these forms 

 and that their absence in Limulus can only be used as a 

 negative argument of little weight. In this connection the 

 conditions figured on PI. XIII, Fig. 88, deserve more detailed 

 study in later stages. 



The presence of salivary glands in the '* Tracheates " and 

 their absence from the " Branchiates " (Crustacea, Limulus) 

 is possibly to be explained by the different method of life of 

 the members of the two groups — aquatic in the latter, ter- 

 restrial in the former. It is, however, to be noted that sali- 

 vary glands have been recognized in Astacus (Lang, '89, p. 

 344), while renewed studies must be made of the so-called 

 salivary glands of the Arachnida before we are certain of 

 their homology with those of the Hexapods. Several organs 

 which have been called salivary glands among the spiders and 

 their allies have been shown to be coxal glands {i.e. nephridia) 

 or poison glands, and it is possible that all of these organs 

 may have different homologies than those indicated by the 

 name usually applied to them. 



