Prof. E. Claparéde on the Structure 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- 
parable 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 Oligocheta 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 Polycheta, likewise, it is only a part of the segmental 
organs that take the part of an efferent 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 Chiaje (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 [ 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 dicecious nature of the immense majority of the Annelida. We 
must, however, not forget that before him Delle Chiaje maintained this 
diceciousness 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., tom. ili. 
p- 100). Baster and Pallas, however, appear to have been the first to 
ascertain positively the diceciousness of an Annelide, Aphrodita aculeata. 
(See Natuurkundige Uitspanningen, &c., Deel ii. p. 68, edit. 1817, and 
Miscellanea Zoologica, 1766, p. 90.) 
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