682 MR J. T. CUNNINGHAM AND MR G. A. RAMAGE ON THE 



fathoms, in mud N.W. and W. of Inchkeith. They were found by sifting the 

 mud, and were always broken; no complete specimen being obtained. Sars 

 found his specimens on the N.W. shores of Norway, some in the Laminarian 

 zone, some at 50 to 60 fathoms, some at 20 to 30 fathoms. Claparede found 

 it in the littoral zone on the coast of Normandy. 



Anatomy. — The ventral nerve cord lies internal to both circular and longi- 

 tudinal layers of muscles, throughout the body : the cord is not in immediate 

 contact with any other organs, but is suspended in the coelom by strands 

 of muscular and connective tissue, which pass from the sides of the sheath 

 surrounding the cord into certain strands connected with the circular 

 muscles. There are no differentiated ganglia ; the cord is of uniform width 

 throughout its length, except where slight constrictions mark the boundary 

 between contiguous somites. The sheath surrounding the cord is fibrous, and 

 contains small muclei. A neural canal runs along the dorsal median line of 

 the cord. On the dorsal side there are no neural cells, but these form a con- 

 tinuous layer at the sides and ventrally, the layer being thickest laterally. The 

 internal core of the cord is composed of minute fibrils. 



The intestine is very narrow, both in the anterior and posterior regions of 

 the body, but especially in the latter. 



The arrangement of the muscles is noticeable. The longitudinal layer is 

 very strongly developed (PI. XLVII. fig. 44). 



DESCRIPTION OF PLATES. 

 Plate XXXVI. 



Fig. 1. Nerine coniocephala, anterior end. 1 a, parapodiura from anterior region, with branchia and 

 produced dorsal lamina ; 1 b, parapodinm from middle region, with branchial cirrus ; 



1 c, uncinus ; 1 d, ripe unfertilised ovum ; 1 e, ovum, with four segments. 



Fig. 2. Nerine cirratulus, anterior end with proboscis everted. 2 a, parapodium and branchial cirrus 

 from anterior region ; 2 b, parapodium and branchia from middle region ; 2 c, uncinus ; 

 2d, anterior end, with proboscis retracted; 2 e, posterior end, dorsal surface; 2 f, longi- 

 tudinal vertical section, showing nephridia and ovaries ; 2 G, larva of Nerine, with 2 

 somites provided with provisional chastas. 



Plate XXXVII. 



Fig. 2 h. Trochosphere of Nerine, dorsal surface, from life, e, Zeiss, Oc. 2, Camera, Feb. 21, 1887; 



2 i, advanced larva of Nerine, dorsal surface ; 2 j, same, ventral surface. 



Fig. 3. ScolecoUjm vuhjaru, anterior end. 3 a, posterior end ; 3 b, parapodium from anterior 

 region, and branchia; 3c, parapodium and branchia from middle region. 



Fig. 4. Spin xrfirtu-nix, anterior end. 4 a, posterior end ; 4 b, uncinus. 



Fig. 5. Leucodore ciliatmt, anterior end. 5 a, posterior end ; 5 b, modified dorsal chaetse of 5th chaetiferous 

 somite ; 5 c, uncinus. 



Plate XXXVIII. 



Fig. 6. Mayelona papillicornis, anterior end, dorsal surface. 6 a, same, lateral surface; 6b, posterior 

 end, dorsal surface ; 6 c, parapodium ; 6 d, uncinus. 



