BRITISH NEMERTEANS, AND SOME NEW BRITISH ANNELIDS. 431 



Fig. 10. Aggregations of fatty granules from the discarded coating of the embryo of B. olivacea. 

 x 210 diameters. 



Plate XII. 



Fig. 1. Transverse section through the proboscis of a Borlasian (Micrura) from St Andrews; a, 

 external coat ; b, great longitudinal muscular layer ; c, belt of circular muscular libres ; 

 d, basement-layer ; e, incomplete series of longitudinal fibres which do not occur in the 

 common species; /, glandular mucous coat; g, peculiar lozenge-shaped portion of longi- 

 tudinal fibres, formed by the splitting and crossing of two bands from the circular muscu- 

 lar coat; g, separated segment at the other pole of the circle. x 90 diameters. 



2. Transverse section of the snout of Borlasia olivacea, somewhat behind that shown in fig. 4. 



PI. X., and through the anterior part of the cephalic fissures. The channel for the 

 proboscis has become more central in position. The superior pigmentary belt (3) is 

 somewhat narrower, and an inferior (4) has now appeared. The central channel has 

 a layer of longitudinal muscular fibres internally, and a powerful series of oblique and 

 circular fibres (2, 2) form a very efficient exterior investment. x 55 diameters. 



3. Transverse section of a specimen of B. olivacea, in which the ova are well developed. 



The shrunken condition of the walls of the digestive cavity (/), with the numerous array 

 of gregariniform parasites, is in strong contrast with the state of the animal after spawn- 

 ing. The specimen had been in spirit for a considerable time before dissection. x 55 

 diameters. 



4. Parasitic ciliated animal from the tissues of the same species. The letters, a, b, c, and d, 



correspond with tbe groups of segments described in the text. x 350 diameters. 



5. The foregoing parasite in an earlier state of development. x 350 diameters. 



6. The last-mentioned specimen subjected to slight pressure, so as to exhibit the segments. 



x 350 diameters. 



7. Posterior end of a young B. olivacea, showing the anal papilla. x 210 diameters. 



8. Transverse section through the post-ganglionic region of Lineus lactea, Mont. MS., show- 



ing the long vascular lacunae (s, s) in front of the oesophageal region. The slice of the 

 proboscis has fallen out of its sheath (o). x 90 diameters. 



9. Stylet-region in Tetrastemma variegatum, somewhat contracted, and with the floor of the 



anterior chamber pouted forwards. The latter condition is more easily seen in Tetras- 

 temma than in 0. alba. x 210 diameters. 



... 10. Fragment of the wall of the digestive chamber-proper, from the living Borlasia olivacea. 

 The cilia mark the inner surface. x 350 diameters. 



... 11. Cells from the digestive cavity of a young Ceplialothrix filiformis. x 700 diameters. 



... 12. One of the pinnate processes of the scale of Stlienelais dendrolepis, Clap. x 90 diameters. 



Plate XIII. 



Fig. 1. Highly magnified view of the anterior end of Ceplialothrix filiformis ( Astemma) ; b, b, bridles 

 of sheath for proboscis. 



2. Arrangement of the vessels at the posterior extremity of Borlasia olivacea. Magnified. 



3. Ovum of Ceplialothrix filiformis immediately after deposition. x 350 diameters. 



1. Flask from the mucous cord of B. olivacea, with two young animals somewhat compressed; «, 

 embryo forced from its ciliated cellulo -granular fatty coating, the bulk of which lies at c ; 

 b, embryo still within the ciliated coating. x 55 diameters. 



5. Young B. olivacea immediately after leaving the flask- shaped capsule; b, opening of the 



cephalic sac of the right side. The other letters as in the adult. x 90 diameters. 



6. Transverse section through the middle of B. olivacea after the second or great region of the 



digestive cavity has attained its full size. The difference between such a view and the 

 indistinct mass formed by the Ommatoplean digestive cavity, after section, is character- 

 istic, x 55 diameters. 

 .., 7. Cellular elements of the wall of the digestive chamber of the same species. x 700 

 diameters. 



8. Pale oily region with germinal vesicle (a), and germinal dot (Jj), in an ovum removed from 



the body of the female B. olivacea. x 35 diameters. 



9. Elements of the glandular papillee of the proboscis of B. olivacea, after their escape into the 



surrounding water. x 700 diameters. 



