102 



NEMERTINEA 



small terminal pore occurs ; this is the external 

 -iv.q opening of the proboscis (Fig. 51, p.p). 



Nemertines are often very diversely and 

 brilliantly coloured, the hues most commonly 

 found being white, yellow, green, deep purple, and 

 various shades of red and pink. The ventral sur- 

 face is usually paler in colour than the dorsal, 

 and the latter is often marked by longitudinal and 

 transverse stripes (Fig. 59) in contrasting colours. 



The whole animal is enveloped in a layer of 

 mucus, which sometimes becomes hardened to 

 form a tube, and this may be still further 

 strengthened by an admixture of particles of 

 sand or earth. 



The body is capable to a great extent of con- 

 traction and extension, a Nemertine many inches 

 long being apt, when irritated or alarmed, to 

 contract itself to the length of not more than 

 half an inch. Hence, unless the animal is kept 

 and carefully watched, a very erroneous idea may 

 be conceived as to its size. 



Anatomy. The body-wall consists of several 

 layers (Fig. 52), which in a typical highly- 

 developed Nemertine are as follows : 



1. An external epidermic layer (ep), consist- 

 ing of ciliated cells, among which are placed 

 numerous unicellular glands. These glands pro- 

 bably secrete the mucus in which the Nemertine 

 is usually enveloped ; their contents when in the 

 body are very highly refracting. The epidermis 

 rests on a basement membrane (b.in). 



2. The two or three muscular layers, arranged 

 as either an external circular and an internal 

 longitudinal, or an inner and an outer circular 

 separated by a longitudinal layer, or, as in the 

 figure (c.m and l.ni), two longitudinal separated 

 by a circular layer. 



3. A fairly thick connective-tissue layer often 

 found letweeii the epidermis and the muscles, into 

 gradually merges (s.). 



FIG. 51.Amphi- 

 porus lacti- 

 Jlorcus Johnst., 

 drawn from the 

 living specimen, 

 from the dorsal 

 surface. Ply- 

 mouth, x 2. 

 e, Eyes ; 0, gen- 

 erative organs ; 

 n.g, nerve gan- 

 glion ; p.p, pro- 

 boscis pore; p, 

 proboscis. 



which latter it 



