NO. 1772. 



ANNELIDS OF THE ARENIC0LIDM—A8HW0RTH. 



15 



L. 



dorsal view of the worm ; their flat faces are well seen on looking 

 at the worm from the anterior aspect. The lateral lobes envelop the 

 smaller median lobe posteriorly and laterally. As seen from the dorsal 

 aspect (fig. 4) the lateral lobes of the prostomium are widely divari- 

 cated, and immediately behind their point of union there is a small 

 median structure (P) which lies in the nuchal groove, its posterior 

 and slightly narrower end being hidden in the median portion of the 

 nuchal organ. This little structure seems to have been regarded by 

 Fauvel, who examined the external characters of the specimen about 

 eleven years ago, as the median lobe of the prostomium,*^ but, as we 

 have already seen, the true median lobe is anterior to the point of 

 union of the lateral lobes (as it is in 

 other species of Arenicola) while the 

 lobe under discussion is posterior to 

 this junction. This structure is the 

 most posterior portion of the prosto- 

 mium, only a very small portion, or 

 none, of which is usually visible, be- 

 cause it is generally almost or entirely 

 hidden in the nuchal organ; the ex- 

 treme protrusion of the prostomium in 

 this specimen has brought this posterior 

 median portion into view. The exami- 

 nation of the internal organs of this 

 worm showed that there are six pairs 

 of nephridia opening on the fourth to 

 the ninth segments, twelve oesophageal 

 glands (six on each side), and that 

 septal pouches are not present. Most 

 carefid examination of the region in 

 which statocysts should be looked for failed to reveal their presence ; 

 to definitely estabKsh their absence it would be necessary to make 

 serial sections of a portion of the anterior end of the worm, but that 

 is, of course, precluded in this case. I can only say, therefore, that, 

 having very carefully searched for the statocysts, as far as was pos- 

 sible in such a valuable specimen, I believe them to be absent. 



We have now the information at our disposal to enable us to deter- 

 mine whether J., pusilla de Quatrefages is henceforward to be regarded 

 as a valid species or whether it should be merged with one of the better- 

 known species. It is clear that the diagnosis given by de Quatre- 

 fages is erroneous, for gills are borne on the eighth and ninth segments. 

 The comparatively high grade of development of the gills mentioned 



Fig. 4.— Dorsal view of the anterior 



END OF "A. pusilla" QUATREFAGES 

 SHOWING THE WIDELY DIVARICATED 

 LATERAL LOBES (L) AND THE MEDIAN 

 POSTERIOR PORTION (P) OF THE PRO- 

 STOMIUM (jyi) FIRST notopodium; 

 (iV.Gfl) NUCHAL GROOVE. X8. 



by de Quatrefages is not a definite character on which to found a 



a "Petit lobe median triangulaire." Mem. Soc. Nation. Sci. Nat. Math. Cher- 

 bourg, vol. 31, 1899, p. 177. 



