28o 



ENTEMAN. 



[Vol. II. 



system are segmental in the first to the sixth, and the second 

 to the seventh segments, the metameric genital strand thus 

 produced subsequently contracting and moving back to occupy 



Fig. 6. 



Fig. 7. Fig. 8. 



Fig. 6. — Three posterior segments of male Xe}i.os Rossii, seen from above. (After Nassanow.) 



d.e., ductus ejaculatorius ; v.d., vas deferens; t., testes ; d.t., digestive tract ; c, coeca. 

 Fig. 7. — Sagittal section of female of Xenos Rossii. (After Nassanow.) m., mouth; b.c, 



brood canal; (5./. , brood funnels ; i)., ova ;/..?'., fat-body; j.^., supra-oesophageal ganglion ; 



i.jf., sub-oesophageal ganglion ; a.g., abdominal ganglion. 

 Fig. 8. — Five stages in the development of a segmental brood funnel. (After Nassanow.) 



<?., ectoderm ; ;«., mesoderm. 



its usual position in the posterior part of the abdomen. The 



sexual organs are thus traceable to a primitive segmental type. 



Similarly the condition in Xenos may be regarded as the reten- 



■ tion of a primitive character, as might be expected in a degen- 



