Prof. E. Claparedc 07i the Sfrvctvre of the Annelida. 355 



was too favourable to his theory. The mistake appears to have 

 been caused in some cases by the presence of ovules in these 

 organs, which are probably concerned in oviposition*. 



Since the investigations of Dr. Williams, the segmental 

 organs have given rise to much controversy. Most recently, 

 M. Ehlers regards them as apparatus destined to conduct out- 

 ward the mature sexual elements ; and this opinion is certainly 

 correct. Besides the facts cited in its support by that anatomist, 

 others will be found in the course of the present memoir. Ne- 

 vertheless this is not the only function of the segmental organs. 

 Thus they exist in the anterior segments of many Annelida in 

 which the ovules and spermatozoids never penetrate into that 

 region. Their wall is often glandular, and histologically com- 

 ])arable with the elements of the kidney in the Gasteropoda 

 {Amphictenea, Pherusea) . Therefore I hardly doubt that these 

 organs also play an excrementitial part. We know also that in 

 the Oligochpeta only a small number of these segmental organs 

 are modified for the purpose of conducting outward the sexual 

 elements, whilst the rest incontestably fulfil other functions. 

 In the Polychffita, likewise, it is only a part of the segmental 

 organs that take the part of an effeient generative apparatus. 



The older authors, who were acquainted at least with the 

 external apertures of the segmental organs, such as Treviranus 

 (who describes them in Aphrodita) and Delle Chiajc (who as- 

 sumes their existence in all Annelida, and mentions them in 

 many species), attributed a very different function to these 

 organs. They regarded them as serving for the introduction of 

 water into the perivisceral cavity. This opinion can no longer 

 be maintained. The direction of the ciliary movement in the 

 calibre of the tube is opposed to it, as also the circumstance 

 that the inner orifice of the segmental organ seems to be 

 wanting in some instances ; at least I believe I have ascertained 

 this to be the case in some Capitellea. 



M. de Quatrefages, who has never been able to see a seg- 

 mental organ, attributes to M. Ehlers and myself the honour of 

 having contributed most to the extension of Dr. Williams's 



* It is chiefly to M. de Quatrefages that we owe the recent demonstra- 

 tion of the dioecious nature of the immense majority of the Annehda. We 

 must, however, not forget that before him Delle Chiaje maintained this 

 dioeciousness in opposition to all his contemporaries, and that in the most 

 formal manner. He knew that the generative organs present the same 

 form in both sexes. According to his observations, the males are less 

 abundant than the females. (See Descrizione e Notomia, &c., torn. iii. 

 p. 100). Baster and Pallas, however, appear to have been the first to 

 ascertain positively the dioeciousness of an Annelide, Aphrodita aculeata. 

 (See Natuurkundige Uitspanningen, &c., Deel ii. p. 68, edit. ISl/, and 

 Miscellanea Zoologica, 17^6, p. 90.) 



24* 



