46 VERMES. 



Order 2. Nemertina (Nemertea). Elongated ciliated worms with a 

 dorsal eversible proboscis (surrounded by nervous commissures), a straight 

 gut terminating in an anus, blood-vessels and spaces (body-cavity), a 

 pair of cephalic pits and two anterior nephridia. Nearly all marine, 

 and with sexes separate. 



A 11 o p 1 a, proboscis devoid of armature, three layers of muscle in body- 

 wall, and development sometimes with metamorphosis (larva of Desor, 

 and Pilidium). Linens longissimus. Borlasia. Pelagonemertes. 



E n o p 1 a (Hoplonemertea), proboscis armed with stylets, two layers of 

 muscle in body-wall, development direct. Nemertes. Tetrastemma 

 obscura, viviparous. Malacobdella. 



