498 RICHAED EVANS. 



of each sac a short duct passes into the posterior outer corner 

 of the uiedian diverticulum of the buccal cavity. 



Shortly before the tubular glands pass into the above- 

 mentioned sacs there is a sudden, well-nmrked change in the 

 characters of the lining cells. The lining of the glandular 

 part in this region consists of short columnar cells with no 

 well-defined cell outlines, and with nuclei in the centre, while 

 the lining of the portion which enters the sacs consists of tall 

 columnar cells with large nuclei situated at their free ends 

 and with well-defined cell outlines. In both respects the 

 lining of the sacs resembles the latter, which is a proof 

 that they are mere diverticula of the ectodermal ducts 

 (fig. 32). The lining of the backAvard diverticulum of the 

 mouth, that is, the so-called common duct of the salivary 

 glands, consists of much shorter cells with nuclei in the 

 centre, but the linings of the two regions pass gradually into 

 each other. 



The sharp distinction between the lining cells shown in 

 figure 32 probably marks the external limit of the meso- 

 dermal portion of the gland. 



Mr. Sedgwick describes the elongated glandular portion 

 as being produced by the backward extension of the duct, 

 and since the duct is mesodermal in origin the gland must 

 be so too (14). If we judge fi-om the histology of the parts 

 in question, there seems to be no doubt but that the tubular 

 gland, which runs along at least two thirds of the length of 

 the body, is mesodermal. Kennel would probably consider 

 it ectodermal, but the histology of ihe salivary glands, the 

 renal organs, the genital organs, and finally of the male 

 accessory glands, all of which appear to be homologous 

 organs, tends to disprove Kennel's view of the nature of the 

 renal and genital ducts, as well as of the salivary duct, from 

 which the salivary gland is produced by a backward exten- 

 sion. 



{d) The Renal Organs : — Renal organs occur in all the 

 leg-bearing segments except the genital one. However, a 

 complete ducb was not found in the last segment provided 



