148 Royal Society: — 



The structure may be examined under the following heads : — 

 Cuticle. — -This chitiuous transparent layer is densest on the snout 

 and anterior region of the body, both being much exposed in the 

 boring-operations. Throughout the rest of the body it attains its 

 maximum thickness over the nerve-cords in the ventral median 

 line. No cilia occur anywhere on its surface, and only faint indica- 

 tions of pores exist in certain regions. Fine motionless palpocils 

 abound ail over the cuticle. 



The Hypodenn forms a very large proportion of the tissues of 

 the flattened snout, the whole region outside the four muscular 

 compartments being occupied by it ; so that, in transverse section, 

 it assumes on each side the shape of a long lanceolate process, 

 which much resembles a leaf with its midrib and veins. Through- 

 out the anterior and posterior regions of the body it forms a com- 

 plete sheath, with various thickenings, and at the tip of the tail 

 ends in two lateral styles, the glandular tissue of which (as in the 

 dorsal and ventral processes) is arranged in a very regular manner. 

 In minute structure the hypoderm much resembles the Nemertian 

 cutis, presenting under pressure in the fresh animal a series of 

 flask-shaped glands or cells, from which the contents escape as 

 clear or granular globules. Moreover, it contains a vast number 

 of bacillary cells, some of which have pigment and a large clear 

 globule. In the hypoderm lie the nervous system and neural 

 canals. 



Muscular System. — The four longitudinal muscles of the spathu- 

 late snout are arranged within a curious framework of chitinous 

 basement-tissue, which in section assumes various shapes — in 

 front being like a pair of spectacles, then a figure of eight, and for 

 a considerable distance very much resembling a crown. This frame- 

 work exercises an important influence on the functions of the part. 

 The central pair of muscles are confined to the snout ; the lateral 

 pass behind the mouth to constitute the ventral longitudinal pair. 

 In the preoral chamber are a strong transverse muscle (acting as 

 the chief approximator of the sides) and a A^ertical muscle. The 

 muscles of the body-wall (besides the pair mentioned) are circular, 

 longitudinal dorsal, vertical, oblique, external or lateral vertical and 

 transverse ventral. Anteriorly all are powerfully developed for 

 the peculiar functions of the region, viz. the compression of the 

 blood-channels and the thrusting out of the proboscis. The muscles 

 of the ninth body-segment are modified so as to form great con- 

 strictors, which have a slightly spiral arrangement. In addition 

 to those of the body-w'all, anteriorly, are the long and short retractor 

 muscles of the proboscis, and various bands acting on the buccal 

 and pharyngeal regions. In the posterior division of the body 

 the transverse ventral muscles become atrophied ; but the dorsal 

 and ventral longitudinal muscles, though constricted at the ninth 

 segment, extend throughout ; and the other muscles of the body- 

 wall are likewise present. 



Di/festive System. — A T-shaped slit leads into the buccal region, 

 then follow pharynx, oesophagus, ventricular division, and intes- 



