Misce lla n eous. 389 



On Exogone (Exotokas, Elders) gemmifera, Pagenst. 



By M. C. Viguier. 



In the course of some investigations upon the Annelida of the Bay 

 of Algiers I have met with some interesting types upon which M. 

 Pagenstecher long ago published a curious memoir *. Upon a Syl- 

 lidian of very small size, to which he gave the name of Exogone 

 gemmifera, this naturalist found a series of young animals which he 

 believed to be inserted above each parapodium in the middle region 

 of the worm. The specimen which presented this appearance being 

 destitute of the bundles of long capillary setae which ordinarily dis- 

 tinguish the sexual generation in the annelids of this group, M. 

 Pagenstecher concluded that it belonged to the agamic generation, 

 and that the larvae originated from buds developed on the spot. He 

 was confirmed in this idea by the observation of three examples 

 with long setae, one of which bore ova in the manner already known, 

 and which he thought to represent the sexual generation. To make 

 up for the insufficiency of his own observations, M. Pagenstecher 

 interpreted the previous observations of (Ersted and Krolm in 

 accordance with his theory. The former had taken the animals 

 with long setae for the males and the others for the females in his 

 E. naidina. The second, in his SylJis pulligera (Syllides puUiger, 

 Clap. ), had seen capillary setae in females still carrying their ova in 

 the cavity of the segments, and thought that in those which carried 

 larvae the long setae had disappeared at the time of the hatching of 

 the ova. Both were supposed to have had before them gemmiparous 

 animals without recognizing their true nature. As to the position 

 of the larvae, it is dorsal according to Krohn and Pagenstecher, ven- 

 tral according to (Ersted. 



At Algiers it is easy to find the type described by M. Pagenstecher ; 

 and although the figures that he has published are defective, it is 

 impossible not to recognize that we have to do with the same species. 

 However, we do not find indicated the absence of dorsal cirri upon 

 the second normal segment. Moreover, in the description of the 

 seta) which compose a parapodium, the two different setae are indi- 

 cated as below the three similar ones. This shows us that the author 

 took the belly for the back, and the ventral cirri, which in fact are 

 not deficient in the second parapodium, for the dorsal cirri. The 

 latter, which are very small, will no doubt have escaped the notice 

 of the author, who does not mention ventral cirri. Further, Ehlers 

 ( 4 Borst enwiirmer '), who separates E. gemmifera from Exogone because 

 of the presence in it of tentacular cirri, and refers it to his genus 

 Exotohis, places in the character of the latter genus "Baucheirren 

 fihlm" It is difficult to distinguish between the dorsal and ventral 

 surfaces if we only examine the animal flattened iu a compressorium. 



* " Untersuchungen iiber niedere Seethiere aus Ctette: I. Exogone 

 gemmifera und einige verwandte Syllidien/' Zeitschr. fiir wiss. Zool. Bd. 

 xii. p. 267. 



