On an Alciopid, a Parasite of Cjdippe densa. 29 



II. — N'ote on an Alcioptd, a Parasite of Cydippe densa, 

 Forshal. By Edwaed Ren£ Clapae^de, Professor of 

 Comparative Anatomy in the Academy of Geneva, and 

 Paul Panceri, Professor of Comparative Anatomy in the 

 Royal University of Naples *. 



[Plate v.] 



The authors, having made in the month of March last obser- 

 vations on the same subject, which agree and are mutually 

 complementary, have determined to publish them in conjunc- 

 tion, and prior to other works, in order to make known sooner 

 the first and perhaps the only observations that have been 

 made on the metamorphosis of the Alcioj)ai'\, and to illustrate 

 this case of endoparasitism, singular among the Annelida J. 



Among the many deep-sea animals which the currents 

 bring into the Gulf of Naples, and which delight as well the 

 resident naturalists as those who resort to these shores from 

 distant countries, one of the numerous and elegant forms 

 of the Beroids is a Pleurobranch, corresponding, as we think, 

 to the Cydippe densa of Forskal, better described by Gegen- 

 baur under the more recent name of G. liormiplwra^. In 

 some individuals of this species, obtained at different periods, 

 there were visible within the gelatinous mass, and also towards 

 the outer surface of the body, some white corpuscles, which at 

 first sight we took for those larvae of Distoma, with the tail 

 armed, which have been described by G. Mliller || as Cercaria 

 setifera, and subsequently by Graeffe as C. thaumantiatis^^ 



* Translated and kindly communicated by A. H. Haliday, A.M., from 

 the 'Memorie deUa Societa Italiana di Scienze natui-ali,' tomo iii. No. 4. 

 Milan, 1867._ 



t An Alciope larva seems to have been seen by Leuckart (Arch. f. 

 Naturg. xxi. 1855); but, to judge from the figure, we are inclined to 

 think it may have been a young animal in the act of reproducing the 

 posterior extremity of the body. 



\ As ectoparasitic or sedentary Annelida may be considered (besides a 

 great number of Hirudined) the Sti/Iaria and the Chcetogastcr of Lxjm- 

 ndus and other Naids, as also the Amphinomid discovered by Fritz Miiller 

 in the cavity of the shell of Lepas anatifera, and refen-ed to by him in his 

 essay * Fur Darwin,' 1864, pp. 29, 30 ; to which we have now to add the 

 Myzostomum of Comatula, according to what Mecznikow has published 

 concerning its development and its position among the Annelida (Zeitschr. 

 f. wissenach. Zoologie, Bd. xvi. 186G). 



§ Studien lib. Organisat. u. Systematik der Ctenophoren (Arch, f, 

 Naturg. Bd. xxii. 1850). [= Cydippe plumosa, Sa.Ts,=Ifor?m'phoi-a plu- 

 mosa, Agassiz. — Note by Tr.] 



II Ueber eine eigenth. Wurmlarve (Arch. f. Anatomic u. Physiologic, 

 1850, p. 497). 



% Beobacht. lib. Radiat. u. Wiu-mer in Nizza (Denkschr. der Schweiz. 

 Naturf. Gesellschaft, Bd. xvii. 1858). 



For further details about these larvae, see Claparede, Beobacht. ub. 



