280 }fi.'<rd7((ueous. 



are found the two lips, while on the dorsal surface, behind the un- 

 paired antenna, is situated the caruncle. The eaiernal antenncp 

 {cmctorxim) are tentacular cirri by reason of their innervation, and 

 Quatrefages (1865) justly contends that they must belong to a 

 rudimentary segment. 



(3n stiidying certain series of forms belonging to tlie family with 

 which Ave are dealing, two tendencies may be remarked in the modi- 

 fication of the anterior extremity : (1) Tlie parapodia of the first 

 three or four segments travel more and more towards the front, so 

 that their axes tend to lie in the sagittal plane of the body ; (2) the 

 mouth and lips travel more and more towards the rear, and the 

 anterior pair of eyes, with the paired antennae, tends to pass to the 

 ventral surface. It is probable that the second tendency is but a 

 result of the first. 



These modifications are exhibited to a very high degree in 

 Fvphrosine. In this genus the caruncle, the unpaired antenna, and 

 the posterior eyes have retained their dorsal position (thej' have 

 even been thrust slightly backwards), but the anterior eyes and the 

 paired antenna? are ventral. Between the paired antennte and the 

 unpaired oigan lies a considerable space, occupied by the terminal 

 projection of the anterior extremity, which corresponds to the very 

 small interval that se])arates the appendages in question in the case 

 of the other Amphinomidoe. Since in Exiphrosine the first segment 

 is normal, the tentacular cirri appear in their primitive guise of 

 parapodial cirri. 



The study of the brain not only justifies the interpretation given 

 to the cephalic lobe of Eujihrosine, but permits us at the same time 

 to comprehend the true n.iture of the appendages. I agree with 

 Hatschck (1893) in considering that the brain of the Polycha3tes 

 provided with cephalic appendages is formed of three distinct regions : 

 the anterior brain innervating the palpi ; the middle brain giving 

 off nerves to the antennse, to the eyes, and furnishing the major 

 portion of the fibres of the commissures ; and finally the posterior 

 brain which innerv-ates the nuchal organ. 



In Evphrosine the brain undergoes the same change of position as 

 the cephahc lobe. The anterior brain is ventral ; it gives off two 

 large nerves, which pass each to the corresponding lip. These 

 organs, formed by evaginations of the dermo-muscular layer, are 

 therefore palpi. They cannot be homologous with the buccal pads 

 (canssinets buccaux) of the Eunicidae, as is supposed by Ehlers 

 (1887), but are homologous with the palpi of those animals, as also 

 of the Aphroditidse. 



The middle brain exhibits great elongation and great lateral 

 compression. Its median region, from being dorsal, has become 

 anterior. From its anterior region, which has become ventral, issue 

 the commissures which run their entire course in a plane that is 

 horizontal, and not more or less vertical as in the case of the other 

 PolychaBtes. From the same region arise the nerves of the anterior 

 eyes and those of the paired anteurte. The nerve of the unpaired 

 antenna and those of the posterior eyes are furnished by the 

 posterior region, which is here dorsal, of the middle brain. 



