NEMERTINEA HAYLTS. 131 



embedded among, the fibres of the outer longitudinal muscle-laver (LM 2 .). The deep 

 primary basement membrane," so conspicuous in L. rurriii/iihix. separating the 

 glandular layer from the musculature, is entirely alisent. 



The outer laver of longitudinal muscles (I'l. II. tigs. _'. 3, 4. ;">. L.M' : . ) is 

 exceedingly thick and well-developed. Its tihres are separated into groups only bv 

 slight partitions of connective tissue, so that under a low power of the microscope the\ 

 appear closely and evenly placed together, and the whole laver lias a verv solid aspect. 

 Between this layer and the circular muscles there is present the usual nerve-plexus 

 (I'l. II, fig. 2. N.I'.), with the two large and well-developed lateral nerve-stems and a 

 small dorsal nerve. 



The circular muscle-layer (I'l. 11, tigs. -2, 4, 5, (AM.), like the outer longitudinal 

 layer, is very stout and solid in appearance. It is succeeded liy a comparatively thin 

 inner longitudinal layer (L.M 1 .). The last two layers together make up a thickness 

 nearly equal to that of the outer longitudinal coat. 



Alinn'iifiiri/ ('nun/. The intestine is U-shaped ill transverse section (I'l. II, fig. 2, 

 Int.), and without marked lateral diverticula. It seems to lie characteristic of this 

 species that the "crypts," or pockets, iu the lining epithelium at least, in the 

 cesophageal portion of the gut form very regular and acute angles. 



Proboscis-sheath ami Proboscis. The proboscis-sheath is larger in diameter. 

 relatively to the size of the whole animal, than that of TJ. ron'/ii/i/f//*. Its lining 

 epithelium rests on (1) a thin basement-membrane, followed liy (2) a thin longitudinal 

 coat of muscle-fibres; (3) a thin circular coat of muscles, connected dorsally with the 

 circular musculature of the body-wall; and (4) another coat of longitudinal muscles, 

 which is in reality part of the inner longitudinal coat of the body-wall. 



The dorsal blood-vessel (PL II, figs. 2, 4, 5, D.V.), or vessel of the rhynchocoele, 

 as it might more descriptively lie called, lies, anteriorly, on the inside of the circular 

 muscles of the proboscis-sheath ; more posteriorly, it sinks through the circular 

 muscle-layer, and eventually comes to lie below it, among the outer longitudinal 

 muscles. It has very thick walls, as compared with the corresponding vessel in 



The proboscis is thin, and its musculature is not strongly developed. In trans- 

 verse section (PI. II, fig. (!) some of the circular muscle-fibres are seen to cross each 

 other dorsally and ventrally (C., (A), and pass outwards to the periphery, as in the 

 common Cerebratulus marginatus. Within the circular layer of muscles there is a 

 nervous layer, containing four large longitudinal nerves (X.). There is no inner 

 longitudinal layer of muscles separating this nervous laver from the lining epithelium. 

 The latter is mainly composed of tall glandular cells. 



Vascular System. The blood-sinuses in the head are arranged on a plan similar 

 in essential points to that of /,. <;iri'ii : /(ifti*, already described; but after the I'-shaped 

 sinus has passed behind the dorsal commissure of the brain, its two arms extend 

 dorsallv and outwards (I'l. 11, Jig. 4. U.S.), so as to embrace the dorsal ganglia and 



x 2 



