416 A. E. Verrill — Marine Nemertecms of Nevj England, etc. 



Mouth ventral, situated behind the ganglions. 



The muscular walls of the body often consist of three layers : 

 outer longitudinal, middle circular, and inner longitiulinal (PI. 

 xxxix, tigs. 17 to 21). In some cases the outer longitudinal layer is 

 lacking (figs, 15 and 16). 



Two or three main vascular trunks ; the vessels generally not so 

 well defined as in the Eno])la, and often having in part the character 

 of wide lacunie, especially anteriorly, 



(Esophagus entirely behind the brain, usually large, long, plicated, 

 and surrounded by a vascular network, or by lacuna?. (PI. xxxix, 

 fig. 22, "v, r). 



Lateral nerve-trunks arise from the outer sides of the lower gan- 

 glions, and are situated between the muscular layers of the body- 

 walls, but they vary in position in the different families. Usually 

 there is a nervous plexus outside of the circular muscular layer. 

 (PI. xxxix, figs. 17, 20, n). 



The s|)ecies are almost all nuirine ; a few inhabit brackish water. 



Suborder I, RHAG-ADOCEPHALA Diesing, 1850 (emeDded). 



Schizonemtrti7ii \iv\\n-Qcht ■, Carus, Fauuie Med., p. 160. 

 Schizonemertea. Hubrecht, Voy. Challenger, xix, p. :i7. 



Head with a deej), longitudinal, ciliated slit, or fossa (pro1>a])ly 

 olfactory in function), on each side, terminating posteriorly in a deep 

 pit or (^luct running inward to the posterior ganglions. (PI. xxxix, 



fig. 22,/; d, d'). 



Mouth large, behind or opposite the posterior ends of the lateral 

 slits and cej)halic ganglions. (Wood-cut 8). 



Lateral nerve-trunks situated between the outer longitudinal and 

 the circular muscular layers of the body-wall. (PI. xxxix, figs. 

 19 to 21). A median dorsal nerve is also usually distinctly developed. 



Three large, longitudinal, vascular trunks, which are usually con- 

 nected by numerous transverse vessels around the intestine, espe- 

 cially posteriorly, 



CEsophagus large, prolonged backward, plicated, and j)rovided with 

 a vascular system, probably having a respiratory function. (PI, 

 XXXIX, figs. 20, 22). 



Many of the species of this group develop directly from the eggs, 

 without a marked metamorphosis, but certain species of Mlcrura 

 (perhaps all) have a peculiar, free-swimming larval form known as 

 P'didium (PI. xxxix, figs. 1 to 6, and wood-cut 7). The embryology 

 of the closely related genus, Cerebratidas, is apparently unknown. 



