638 THE ANIMAL KINGDOM. 



A ciliated canal leads inwards from each of them and enters the cerebral 

 ganglia in C. inexpectata^ or their posterior or third lobes in Schizo- and 

 Hoplonemertea 1 . In the Schizonemertea the groove is longitudinal and 

 deep ; in most Hoplonemertea transverse and often complicated by the 

 addition of short longitudinal grooves present also in the Palaeonemertean 

 Polia 2 . The ciliated canal of Hoplonemertea is bifurcate. 



The aperture by which the proboscis is extruded is anterior and terminal 

 as a rule, and rarely lies within the mouth (Akrostomum, Geonemertespalaensis, 

 Malacobdella, Monopord). It leads into a narrow canal. The proboscis 

 proper commences just anteriorly to the ganglia. It is tubular, and is 

 contained within a proboscis-sheath. The walls of the two structures are 

 continuous in front, but elsewhere they are separated by a cavity filled with 

 a liquid in which are suspended fusiform corpuscles, tinged with haemo- 

 globin in Cerebratulus urticans. This cavity is completely closed. It is 

 furnished in Drepanophorus with paired lateral diverticula commencing at 

 the level of the nerve ganglia. The sheath lies dorsally to the diges- 

 tive tract and usually reaches the posterior extremity of the body. Some- 

 times, e. g. Carinella, N emeries carcinophila, it is extremely short. It has 

 muscular walls, usually an outer circular and an inner longitudinal layer, 

 whilst its cavity is lined by an epithelium. The proboscis also has muscular 

 walls, an external and internal circular with an intervening longitudinal 

 layer in Palaeo- and Schizo-nemertea \ an outer and inner longitudinal layer 

 with an internal and circular layer in Hoplonemertea. The longitudinal 

 muscles are continued beyond the posterior end of the proboscis as the 

 retractor muscle, which is affixed to the sheath somewhere near its middle 

 region. Numerous longitudinal nerves occur in the proboscis, as in Amphi- 

 porus and Drepanophorus (Hoplonemertea), or a nervous sheath, as in Cere- 

 bratulus (Schizonemertea). The proboscis appears to be everted by the 

 contraction of the sheath upon its contained liquid, but its eversion is only 

 partial. The epithelium lining it is derived from the ectoderm. The surface 

 of the eversible region is often covered with adhesive glandular papillae ; its 

 epithelium sometimes contains nematocysts as in Carinella, Cephalothrix, 

 Borlasia, and especially Cerebratulus. The limit of the eversible region 

 in Hoplonemertea is marked by an internal constriction due to a great 

 development of muscular tissue (the muscular bulb), surrounding a cavity 

 or reservoir, which communicates with both the eversible and non-eversible 

 sections of the organ. A central, partially calcareous stylet, pointed, or 

 in Drepanophorus serrated, is implanted close to the outer opening of the 

 reservoir ; and on either side of it a narrow duct leads to a single small 



1 Hence they have been supposed to possess a respiratory function in relation with the brain, 

 especially in Schizonemertea, where haemoglobin exists in the nervous substance. 



2 The Palaeonemertean Valencinia has ciliated canals, but no grooves. 



