46 DK. p. H. CARPENTEE ON CEETAIN" POINTS 



licemal system, aud to regard the remainder as mainly excre- 

 tory in character, partly, of course, through its plastidogenic 

 functions. Its relations to the ambulacral system are important 

 in this respect, aud have been well expressed by Perrier* : — 



" L'appareil plastidogene est, en grande partie, un centre formateur d' ele- 

 ments anatomiques ; il est a remarquer que, d'une part, il contracte des rapports 

 intimes de contiguite avec l'appareil ambulacraire qui communique, en general, 

 avee I'exterieur, et que, d'autre part, il peut recevoir directement de l'appareil 

 absorbant, quand il existe, des matieres assimilables."' 



It is almost needless to remark that the communication with 

 the exterior is effected by the water-pores ; aud in this rela- 

 tion some recent observations of Ei eld's t are especially inter- 

 esting. Por he has discovered the presence in Bipinnaria of 

 " a stage with bilaterally symmetrical water-pores, homologous 

 in their mode o£ origin, and probably in function, with ne- 

 phridia." 



I have a strong conviction that further researches on Balano- 

 glossus and CephalocUscus, to say nothing of the Tunicates and 

 Amphioxus, will throw considerable light on the comparative 

 morphology of these intimately associated ambulacral and plasti- 

 dogenic systems of Echinoderms ; while the relations of the latter 

 to the genital organs, on which Perrier lays so much stress, afford 

 an additional reason for thinking that the osculum of the mono- 

 trematous Cystids performed a triple function, as suggested above 

 on pp. 27-32. Beddard's discovery of anal nephridia in Acanfho- 

 drilus onuUiporus is very suggestive in this connection ; and he 

 has also shown reasons for thinking that in this type "the gen- 

 ital funnels and a portion at least of the ducts are formed out 

 of nephridia "J. He further points out that at one stage of 

 development of this worm the nephridium branches and becomes 

 segregated " into several almost detached tracts, communicating 

 with the exterior by their own ducts." These are strongly sug- 

 gestive of the multiple water-pores of an Echinoderm ; while in 

 anew Eudrilid recently studied by Beddard§ "the neiDhridial 



* Ihid. p. 73. 



t " Contributions to the Embryology of Asterias vulgaris,^' Johns Hopkins 

 Univ. Circ. vol. x. 1891, No. 88, pp. 101-103. 



I " On the Homology between Grenital Duets and Nephridia in the Oligo- 

 chseta," Proc. Eoy. Soc. 1890, vol. xlviii. p. 455. 



§ " Preliminary Notice of a New Form of Excretory Organs in an Oligo- 

 chaetous Annelid," Proc. Eoy. Soc. 1891, vol. xlix. p. 310. 



