12 



WiLLEY has made probable in the case of ParaperipatKS novae- 

 hritanniae. In P. capensis the trophic vesicle is nnich reducod, biit, 

 as Sedgwick ') has shown, the dorsal ectoderni has preserved the 

 function of resorbing food raaterial. A perfectly analogous pheno- 

 monon in fact is seen in anotlier gronp of terrestrial descendents of 

 the Polychaeta, viz. the Oligochaeta: the embryo oï Lnmhykus^\N\v\Q\i 

 generally is regarded as a modified trochophora, in the dcvolop- 

 ment of a large vesicle reminds strongly of the condition found 

 in Peripatopsis. And in Lumbricus^ as in Peripatopsis^ the "em- 

 bryonic gut is enlarged and its wall applies itself against the 

 ectoderm. However, in the case of LNinhricus the food is taken 

 up from the egg-cocoon instead of the uterus, and by the mouth 

 instead of through the body wall. We thus find here two different 

 methods, in which the trochophora has accommodated itself to 

 the conditions, modified by terrestrial life. 



In Peripatojisis SedgiricM Pure. and in Paraperipatus novae- 

 hritanniae Willey, by the ontogenetic reduction of the caudal part 

 of the trophic vesicle even a striking resemblance with the Pohj- 

 gordius-tv ocho'^hova. is found ^). 



If it is allowed to derive from the trophic vesicle of the Ony- 

 chophora the „dorsal organs" of Scolopendra and some Insects 

 and Crustaceans, as is suggested by Willey and Heymons ^), then 

 these organs finally can be deducod from the cephalic vesicle of 

 the trochophora. By this suggestion the peculiarities of the dorsal 

 organs in Insects, pointed out by Heymons, become intelligible : 

 that the dorsal organs always are found in the nuchal region and 

 that the cgg-yolk of Myriapoda and Insects is accumulated prin- 

 cipally in the cephalic region, is explained by the position of 

 the cephalic vesicle of the Polychaetan ancestors with regard to 

 the trunk; and the rosorption or throwing off of the mentioned 

 organs is a reminiscence of the same phenomenon in PohjgonUus ^). 



1) 1. c. (1887). 



2) See f. i. fig. 34 of Willky, 1. c. (1898), reproiluceil iu Wii.ley (1899), %. 3A. 



3) Die Eutwicklungsgescliiclite der Scolopciider. Zoologiea, H. 33, 1901. 



4) WoLTEKECK. Tiochophoni-Stiulicn. L Zoologica, 11. 34, 1903. 



