206 



ONYCHOPHORA. 



portant changes to be observed in the cephalic and maxillary segments. In 

 the latter the nephridia have degenerated ; traces of them only are said to 

 be found (v. Kennel). In the cephalic segment, on the contrary, the two 

 segmental cavities (in early stages) are said still to open outward through 

 canals (Sheldon, No. 12, Pt. ii.). v. Kennel and Sedgwick describe a 

 (canal-like) continuation of the primitive cephalic cavity which descends on 

 the outer side of the ectodermal thickening (rudiment of the nervous system) 

 and fuses with the ectoderm, immediately in front of the jaws (Sedgwick) ; 

 according to L. Sheldon, indeed, it even opens outward at this point. This 

 canal has been considered homologous to the canal of the nephridia. According 

 to Sedgwick, it therefore belongs to the lateral portion of the first primitive 

 segment. We cannot clearly make out, from the figures given, the relation 

 of this lateral portion to the coelomic cavity of the antennae. We therefore 

 refrain from discussing the position of this efferent canal as conrpared with 

 those of the other nephridia, and merely point out that a remarkable change 

 in the position of the nephridium towards the limb must have taken place if 

 this canal is really the nephridial canal of the so-called cephalic segment, and 

 if our former assumption that the antennae of Per (pectus are transformed limbs 

 is correct (c/. p. 186). 



The Salivary Glands. 



According to v. Kennel and Sedgw t ick, who agree on this point, 

 there can be no doubt that the paired gland -which opens into the 

 buccal cavity through a short, common duct arises from the 

 nephridia of the segment carrying the oral papillae. These ducts 

 develop in the same way as the undoubted nephridia. They originate, 



after the separation 

 of the dorso-median 

 part, from the lateral 

 portions of the primi- 

 tive segments which 

 develop an external 

 aperture (Fig. 92, no, 

 and 93, sp, p. 184). 

 Their furtherdevelop- 

 ment is peculiar only 

 in so far that the 

 canal, at the point 

 where it passes into 

 the terminal sac, 

 begins to lengthen posteriorly (Fig. 103 .4), so that a long, blind 

 tube arises at this point (Fig. 103 D, k). This tube gives origin to 

 the principal part of the salivary gland ; it, however, retains through- 

 out life the vesicular portion of the rudiment (s) corresponding to 

 the terminal sac (v. Kennel, Sedgwick). The connection of the 



Fig. 103.— Formation of the salivary glands of 7'. capensis 

 (after Sedgwick), k, canal of the gland; n, nephridial 

 canal ; s, terminal sac, the walls of which in A appear 

 thinner than in 1'.. 



