148 HOMOLOGIES. 



a frilled appearance, from the rugae, which, as in the Nemerteans, often assume an arborescent 

 appearance, owing to the extrusion (under pressure and preparation) of their cellular and granular 

 elements. The wall of the canal is somewhat thinner in front, while the glandular lining is 

 largely developed. Behind the branchial region, however, the following structure is clearly 

 seen : — Externally the radiating fibres from the outer coat of the body- wall pass into a well- 

 marked layer of circular muscular fibres, upon which the continuous basement-membrane and 

 its glandular lining rest. The latter is thinner than in front. The structure on the whole closely 

 approaches the Nemertean digestive tract. 



Kowalewsky mentions that the surface of the digestive chamber is richly ciliated. His 

 specimens occurred on sandy ground, as might be expected from the nature of their food. 



Circulatory system. 



Two vessels only could be satisfactorily made out by an examination of the specimens. A 

 large longitudinal dorsal vessel lies over the fibrous band connecting the branchial septal rods 

 across the median furrow. At this point it has externally only the circular muscular coat, the 

 basement-membrane and cutaneous tissues, since there is a hiatus in the longitudinal muscular 

 layer. The vessel is continued to the posterior end of the specimen over the wall of the digestive 

 tract. Exactly in the median line on the ventral surface a similar vessel occurs, with the same 

 relations to the cutaneous and alimentary textures. Both trunks have distinct walls. Besides 

 the elaborate arrangement of vessels in connection with the branchial lamellae, Kowalewsky shows 

 a lateral vessel on each side, and various minute twigs from the larger trunks. 



A single imperfect example of the other form of Balanoglossus was dredged by Mr. Jeffreys 

 as above mentioned. In general features and size it resembles the foregoing, but certain ana- 

 tomical differences merit special notice. 



The "Proboscis" consists of a bluntly conical mass, which has lost its cutaneous elements. 

 Externally, instead of the basement-membrane and circular fibres of the former type, there is a 

 coat of longitudinal fibres, or, rather, of fibres whose direction is chiefly longitudinal, for they 

 are felted firmly together. Within is a belt of circular fibres, from which the vertical lamellae of 

 the central region spring. The lamellae consist of fleshy columns, which are fixed to the outer 

 wall all round, but have a free margin internally. In transverse section, thus, the region some- 

 what resembles the kind of fruit called hesperidium, such as that of the orange, only the carpels 

 are enormously increased. The columns are composed of densely felted fibres — longitudinal, 

 oblique, and radiating, besides circular fibres towards the inner free margin. The whole must 

 therefore form a powerful squeezing or propelling organ, after the manner of the heart of the 

 higher animals. This region is attached to the body by an elongated, chitinous, process which 

 has a broad basis at the mouth, and sends four divergent chitinous spurs into the tissues for 

 support, the posterior pair coursing along the borders of the dorsal valves or lips, as in the 



