EXOGONE. 149 



Group L— EXOGONEA. 



Small syllids, with ventral cirri; palpi fused throughout. Segments few and 

 variable. Appendages short. Proboscis straight. Bristles with simple tips to terminal 

 pieces. Reproduction generally direct; rarely by stolons (Malaquin). 



Genus XLV. — Exogone, Mag. (Ersted, 1845. 



Head composed of two distinct segments ; palpi prominent, fused ; three clavate 

 tentacles fixed to the middle of the head; eyes four; one pair of tentacular cirri (short) ; 

 ciliated pits at the posterior part of the cephalic segments. Body small, linear, of a fixed 

 number of segments. Proboscis short, with a single tooth anteriorly ; lateral casca of the 

 stomach small. Two clavate or filiform anal cirri. Feet small, papilliform ; dorsal and 

 ventral cirri sub-equal, clavate, or conical. A single fascicle of falcate bristles in the 

 female ; in the male, all the segments (the first eight excepted) with falcate and long 

 capillary bristles. Reproduction direct. Ova borne on the dorsum or on the ventral 

 surface, with embryos and larvae in the latter case attached near the segmental orifice. 



This group received a notable contribution from the late distinguished anatomist of 

 Wiirzburg, viz. Professor Kolliker, 1 who, in 1845, appended to a paper, by his friend 

 H. Koch, in the f Xouveaux Mem. de la Soc. helvet.,' viii, an account of three forms from 

 Naples, viz. Exogone (Erstedi, Exogone cirrata, and Cystonereis Edwardsi. The first has 

 two pairs of tentacles, eggs in sacs at the sides, and long swimming-bristles. The second 

 has the palpi apparently fused at the base, two pairs of tentacles, and also eggs in sacs at 

 the sides. The third has four pairs of tentacles, no visible palpi, and the eggs are borne 

 ventro-laterally. None of these correspond with Professor Graham Kerr's form from the 

 Clyde with eight ovigerous sacs. 



Considerable confusion has occurred in this group from the imperfect descriptions of 

 authors. Thus the Exogone Kefersteinii of Claparede 3 appears to be Exogone gemmifera, 

 whilst Ehlers, misled by the supposed absence of the ventral cirri, constituted a new 

 genus, ExotoJcas, for the inclusion of both as separate species. Claparede's genus, 

 Poedophylax 3 is in the same position as the Exotohas of Ehlers, both referring to Exogone. 

 The examples of the genus have hitherto been so rarely procured in this country that 

 much yet remains to be done both in synonymy and investigation of structure. 



The genus seems to be cosmopolitan in its distribution, ranging from the Antarctic 

 seas northward, a form very similar to Grubea pusilla, and bearing ova on the dorsum, 

 for instance, occurring at Kerguelen, and entangled amongst the bristles of Loetmonice 

 producta, just as an Irish member of the group was found on Aphrodita aculeata. It is 

 probable that considerable additions will yet be made to the group in British waters, 

 especially on the southern and western coasts. 



1 ' Nachwort zu dem vorhergehenden aufsatze/ op. cit., p. 13. 



2 'Beobacli. ueb. Anat. u. Entwickl./ p. 42, Taf. xii, f. 3—6. 



3 ' Annel. Nap./ p. 210. 



