272 NEMERTEA. 



proboscis is unarmed and opens with the mouth. There is a dorsal vessel, and 

 two lateral. The proboscis-sheath reaches to the anus. Malacobdella Blainv. , 

 in the mantle-cavity of various marine Lamellibranchs. 



Order 4. HETERONEMEKTINI. 



The lateral nerves are in the dermal muscles ; they lie outside the circular 

 muscles. The body-wall consists of ectoderm, dermis, an outer longitudinal 

 layer of muscles (which is not present in the other orders), a circular and an 

 internal longitudinal muscular layer. The diagonal muscles, if present, lie 

 between the circular and outer longitudinal. The mouth is behind the brain. 

 There is no caecum. The proboscis is unarmed. 



Fam. 1. Eupoliidae. There are usually no lateral cephalic slits. The canal 

 of the lateral organ opens either directly to the exterior, or into a shallow 

 ventral slit. Eapolia Hubrecht ; Poliopsis Joubin. ; Valencinia Quatrefages. 



Fam. 2. Lineidae. The body is more or less flattened. There is a deep 

 longitudinal lateral fissure on each side of the head. A ciliated groove leads 

 from the bottom of the fissure into the posterior lobe of the ganglion. The 

 nervous tissue is tinged with haemaglobin. Development often by ciliated 

 larvae. Linens Sow. (Fig. 225) ; L. marinus Mont.; L. longissimus Sim., sea- 

 long-worm ; Borlasia Oken ; Euborlasia Vaill. ; Micrura, Ehrbg. ; Cerebratulus 

 Renier ; Langia Hubrecht, the margins of the body slightly frilled. 



Fio. 2-25.Lineus sanguineus (after Me Intosh). 



